Metabolic syndrome contributes to the pulmonary arterial dysfunction in pulmonary hypertension in heart failure with preserved ejection fraction

Background

Many Heart Failure with preserved Ejection Fraction (HFpEF) patients have metabolic syndrome and develop Exercise Induced Pulmonary Hypertension (EIPH). The pathogenesis of EIPH in HFpEF remains unclear as there is no rodent model. As the SGLT2 inhibitor Empagliflozin improves clinical outcome in patients with type 2 diabetes and cardiovascular risk, we tested its effect on EIPH in a novel rat model of HFpEF.

Methods

Obese ZSF1 (HFpEF model) with leptin receptor mutation have metabolic syndrome and received the VEGF-inhibitor SU5416 to stimulate PH (Obese + Sugen). Half also received Empagliflozin (0.2 mg/kg/day) in drinking water from 8 to 22 weeks old. Lean ZSF1 lacking the mutation served as controls. During treadmill exercise, right/left ventricle (RV/LV) hemodynamics were evaluated via catheters. Pulmonary artery vascular smooth muscle cells (PAVSMC) prepared from normal or diabetic patients were cultured in standard media, or with Palmitate acid, Glucose and Insulin (PGI) to induce metabolic stress. Flow cytometry was used to evaluate reactive oxygen species (ROS) in mitochondria (Mitosox) or cytoplasm (CellROX).

Results

Relative to Lean, Obese + Sugen had increased body weight and HgA1C (Fig. 1A). Relative to Lean and at rest, Obese + Sugen showed mildly elevated RVSP and LVEDP. After exercise, LVSP and LVEDP rose similarly in Lean and Obese + Sugen. However, after exercise, Obese + Sugen showed a markedly greater increase in RVSP and exercise intolerance consistent with EIPH (Fig. 1B). In MR imaging of PA, Lean showed dobutamine (5 μg/kg/min)-induced PA dilation, which was not seen in Obese + Sugen (Fig. 1C). Protein levels of sGCβ1 (key regulator of PA relaxation) and its transcription factor (NFYA) both were decreased in PA from Obese + Sugen relative to Lean (Fig. 1D). Obese + Sugen + SGLT2 inhibitor treated rats showed marked improvements metabolic syndrome (body weight, HgA1c), exercise induced increase in RVSP, PA response to dobutamine, and increased NFYA and sGCβ1 expression (Fig. 1A–D). We observed greater ROS-induced DNA damage (8-OHdG staining) (Fig. 1E) and mitochondrial complex I, III, and IV activity in Obese + Sugen PA that was normalized in Obese + Sugen + SGLT2 inhibitor (Fig. 1F), suggesting a role of ROS in EIPH. Control human PAVSMC treated with PGI media showed elevated cytoplasmic and mitochondrial ROS, associated with increased mitochondrial complex I, III, IV and V activity (Fig. 1F, G). PGI media also accelerated the degradation of NFYA RNA and protein level in a manner mimicked by H2O2, and prevented by catalase/SOD (Fig. 1H, I), suggesting PGI-induced ROS enhanced NFYA degradation. Diabetic human PAVSMCs cultured in normal media resembled PGI-treated normal cells with respect to sGCb1 and NFYA expression, and in response to catalase/SOD (Fig. 1H, I).

Conclusions

In this PH-HFpEF model, metabolic syndrome contributes to PA dysfunction and EIPH through mitochondrial dysfunction and enhanced ROS, which were improved by Empagliflozin treatment.

Figure 1

Funding Acknowledgement

Type of funding source: None

Issues Critical to the Successful Application of Cryosurgical Ablation of the Prostate

The techniques of present-day cryosurgery performed with multiprobe freezing apparatus and advanced imaging techniques yield predictable and encouraging results in the treatment of prostatic and renal cancers. Nevertheless, and not unique to cryosurgical treatment, the rates of persistent disease demonstrate the need for improvement in technique and emphasize the need for proper management of the therapeutic margin. The causes of persistent disease often relate to a range of factors including selection of patients, understanding of the extent of the tumor, limitations of the imaging techniques, and failure to freeze the tumor periphery in an efficacious manner. Of these diverse factors, the one most readily managed, but subject to therapeutic error, is the technique of freezing the tumor and appropriate margin to a lethal temperature [Baust, J. G., Gage, A. A. The Molecular Basis of Cryosurgery. BJU Int 95, 1187–1191 (2005)]. This article describes the recent experiments that examine the molecular basis of cryosurgery, clarifies the actions of the components of the freeze-thaw cycle, and defines the resultant effect on the cryogenic lesion from a clinical perspective. Further, this review addresses the important issue of management of the margin of the tumor through adjunctive therapy. Accordingly, a goal of this review is to identify the technical and future adjunctive therapeutic practices that should improve the efficacy of cryoablative techniques for the treatment of malignant lesions.

Progress toward Optimization of Cryosurgery

Cryosurgery for diverse neoplastic and non-neoplastic diseases has expanded in applicability in recent years, especially since intraoperative ultrasound became available as a method of monitoring the process of tissue freezing. However, persistence of disease after presumably adequate cryosurgical treatment has disclosed deficiencies in the technique, perhaps due to faulty application of the freeze-thaw cycles or due to shortcomings in the imaging method. Clearly cryosurgical technique is less than optimal. The optimal dosimetry for tissue freezing, the recent improvements in imaging techniques, and the need for adjunctive therapy are defined in this review, which assesses the progress toward improving the efficacy of cryosurgery.

Re-purposing cryoablation: a combinatorial 'therapy' for the destruction of tissue

It is now recognized that the tumor microenvironment creates a protective neo-tissue that isolates the tumor from the various defense strategies of the body. Evidence demonstrates that, with successive therapeutic attempts, cancer cells acquire resistance to individual treatment modalities. For example, exposure to cytotoxic drugs results in the survival of approximately 20-30% of the cancer cells as only dividing cells succumb to each toxic exposure. With follow-up treatments, each additional dose results in tumor-associated fibroblasts secreting surface-protective proteins, which enhance cancer cell resistance. Similar outcomes are reported following radiotherapy. These defensive strategies are indicative of evolved capabilities of cancer to assure successful tumor growth through well-established anti-tumor-protective adaptations. As such, successful cancer management requires the activation of multiple cellular 'kill switches' to prevent initiation of diverse protective adaptations. Thermal therapies are unique treatment modalities typically applied as monotherapies (without repetition) thereby denying cancer cells the opportunity to express defensive mutations. Further, the destructive mechanisms of action involved with cryoablation (CA) include both physical and molecular insults resulting in the disruption of multiple defensive strategies that are not cell cycle dependent and adds a damaging structural (physical) element. This review discusses the application and clinical outcomes of CA with an emphasis on the mechanisms of cell death induced by structural, metabolic, vascular and immune processes. The induction of diverse cell death cascades, resulting in the activation of apoptosis and necrosis, allows CA to be characterized as a combinatorial treatment modality. Our understanding of these mechanisms now supports adjunctive therapies that can augment cell death pathways.

Mechanisms of cryoablation: clinical consequences on malignant tumors

While the destructive actions of a cryoablative freeze cycle are long recognized, more recent evidence has revealed a complex set of molecular responses that provides a path for optimization. The importance of optimization relates to the observation that the cryosurgical treatment of tumors yields success only equivalent to alternative therapies. This is also true of all existing therapies of cancer, which while applied with curative intent; provide only disease suppression for periods ranging from months to years. Recent research has led to an important new understanding of the nature of cancer, which has implications for primary therapies, including cryosurgical treatment. We now recognize that a cancer is a highly organized tissue dependent on other supporting cells for its establishment, growth and invasion. Further, cancer stem cells are now recognized as an origin of disease and prove resistant to many treatment modalities. Growth is dependent on endothelial cells essential to blood vessel formation, fibroblasts production of growth factors, and protective functions of cells of the immune system. This review discusses the biology of cancer, which has profound implications for the diverse therapies of the disease, including cryosurgery. We also describe the cryosurgical treatment of diverse cancers, citing results, types of adjunctive therapy intended to improve clinical outcomes, and comment briefly on other energy-based ablative therapies. With an expanded view of tumor complexity we identify those elements key to effective cryoablation and strategies designed to optimize cancer cell mortality with a consideration of the now recognized hallmarks of cancer.

Temperature-dependent activation of differential apoptotic pathways during cryoablation in a human prostate cancer model

BACKGROUND

Critical to the continual improvement of cryoablation efficacy is deciphering the biochemical responses of cells to low-temperature exposure. The identification of delayed-onset cell death has allowed for the manipulation of cellular responses through the regulation of apoptosis. We hypothesized that in addition to delayed apoptotic events associated with mild subfreezing temperatures (10 to -25 °C), cells exposed to ultra-low temperatures (<-30 °C) may undergo rapid, early-onset apoptosis.

METHODS

Human prostate cancer model and cells (PC-3) were exposed to temperatures of -60, -30 and -15 °C to simulate a cryoablative procedure. Using a combination of flow-cytometry, fluorescent microscopy and western blot analyses, samples were assessed at various times post thaw to identify the presence, levels and the pathways involved in cell death.

RESULTS

Exposure to temperatures <-30 °C yielded a significant apoptotic population within 30 min of thawing, peaking at 90 min (~40%), and by 6 h, only necrosis was observed. In samples only reaching temperatures >-30 °C, apoptosis was not noted until 6-24 h post thaw, with the levels of apoptosis reaching ~10% (-15 °C) and ~25% (-30 °C) at 6 h post thaw. Further, it was found that early-onset apoptosis progressed through a membrane-mediated mechanism, whereas delayed apoptosis progressed through a mitochondrial path.

CONCLUSIONS

These data demonstrate the impact of apoptotic continuum, whereby the more severe cryogenic stress activated the extrinsic, membrane-regulated pathway, whereas less severe freezing activated the intrinsic, mitochondrial-mediated path. The rapid induction and progression of apoptosis at ultra-low temperatures provides an explanation as to why such results have not previously been identified following freezing. Ultimately, an understanding of the events and signaling pathways involved in triggering apoptosis following freezing may provide a path for selective induction of the rapid-onset and delayed programmed cell death pathways in an effort to improve the overall cryoablation efficacy.

Cold-Storage of Synthetic Human Epidermis in HypoThermosol

There is a growing need for engineered tissues in a wide variety of medical applications and as alternatives to animal tissues for in vitro toxicology testing. While techniques for the preparation of a variety of synthetic tissue constructs have been devised, little attention has been focused upon the optimum conditions necessary for storage and shipping of these tissue devices. This study investigates the effects of hypothermic storage on synthetic human epidermis (EpiDerm, MatTek Corp., Ashland, MA) and specifically examines the quality of storage in keratinocyte growth medium (KGM), a standard skin culture medium, compared with storage in HypoThermosol, a new hypothermic preservation solution. EpiDerm samples were immersed in HypoThermosol for 1 to 13 days at 4 degrees C and were assayed using the noninvasive, viability indicator dye, Alamar Blue (AB). Samples immersed for 1 to 9 days in HypoThermosol retained their viability subsequent to warming to 37 degrees C and for at least 7 days thereafter in culture. During this time samples previously stored in HypoThermosol continued to generate a stratum corneum and their ultrastructural characteristics were similar to EpiDerm that were not exposed to hypothermic solutions. This profile, however, was not apparent in EpiDerm maintained for 1 to 13 days in KGM and subsequently warmed. These samples appeared viable immediately upon warming in most cases, but viability was not retained thereafter. EpiDerm maintained in KGM and allowed to recover at 37 degrees C appeared necrotic and failed to continue to differentiate. The conclusions of this study are the following: (1) HypoThermosol protects the viability of EpiDerm during cold-storage, (2) HypoThermosol preserves EpiDerm's ability to differentiate subsequent to warming, and (3) the inferior preservation of samples stored in KGM was most apparent 24 h after warming.

Experimental cryosurgery investigations in vivo

Cryosurgery is the use of freezing temperatures to elicit an ablative response in a targeted tissue. This review provides a global overview of experimentation in vivo which has been the basis of advancement of this widely applied therapeutic option. The cellular and tissue-related events that underlie the mechanisms of destruction, including direct cell injury (cryolysis), vascular stasis, apoptosis and necrosis, are described and are related to the optimal methods of technique of freezing to achieve efficacious therapy. In vivo experiments with major organs, including wound healing, the putative immunological response following thawing, and the use of cryoadjunctive strategies to enhance cancer cell sensitivity to freezing, are described.

Cryoablation induces necrosis and apoptosis in lung adenocarcinoma in mice

This study evaluated cryoablation on subcutaneously transplanted tumors of lung adenocarcinoma LA795 in T739 mice in vivo, in an effort to assess the feasibility of cryoablation in treatment of NSCLC. Subcutaneously transplanted lung adenocarcinoma LA795 was implanted into T739 mice yielding tumors of approximately 2.5 cm in diameter. Following cryoablation, the various modes of cell death were studied: necrosis in the central frozen zone by light microscopy and apoptosis in periphery of the frozen zone by in situ end labeling (TUNEL). Bc1-2 and bax expression were detected by immunohistochemical SABC procedures, and the cleavage and activation of Caspase 3 and PARP in peripheral zone by Western blot. We find that in central cryoablated zone, necrosis was the dominant mode of cell death occurring at three hours and four days post-thaw. The first three-hour necrosis peak involved approximately 47% of the tumor while the four-day peak increased in volume to 68% of the tumor. In peripheral cryoablation zone, definite cell apoptosis could be observed by morphological examination under light microscope and TUNEL staining, peaking at 8-16 h after cryoablation. Immunohistochemical results yielded little change in bcl-2 protein expression before and after cryoablation. However, bax protein expression was up-regulated significantly after cryoablation. In addition, cleavage and activation of Caspase-3 and PARP occurred in the peripheral freeze zone after the treatment. It indicated that Cryoablation efficiently induces cell death both by necrosis and apoptosis. Cryoablation appears to induce apoptosis in the peripheral freeze zone through the intrinsic mitochondrial caspase pathway based on bax upregulation. This observation allows us to suggest that cryoablation may be combined with chemotherapy to increase cancer destruction.

Targeted induction of apoptosis via TRAIL and cryoablation: a novel strategy for the treatment of prostate cancer

Adjuvant therapies contribute to the successful treatment of cancer. Our previous reports have shown that combining cryoablation with cytotoxic agents enhances cell death. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytotoxic agent that preferentially induces apoptosis in a variety of human cancer cells. Human prostate cancer cells (PC-3) are resistant to many cytodestructive agents, including cryoablation and TRAIL. Here, we evaluated the effects of TRAIL combined with cryoablation on PC-3 and normal prostate (RWPE-1) cell death. Exposure of PC-3 cells to freezing (-10 degrees C) or TRAIL (500 ng/ml) results in minimal cell death, whereas a complete loss of viability is observed with the simultaneous combination. The synergistic effect was found to be due to a marked increase in apoptosis. Western blot analysis revealed a significant level of caspase-8 and -3 cleavage between 12 and 24 h post-exposure. Caspase activation assays provided similar results and also indicated a role for caspase-9. Inhibitors to caspase-8 and -9 along with a pan-caspase inhibitor were incorporated to determine which pathway was necessary for the combined efficacy. Inhibition of caspase-8 significantly blocked the combination-induced cell death compared to cells that did not receive the inhibitor (63% compared to 10% viable). The addition of the caspase-9 inhibitor resulted in only a minimal protection. Importantly, the combination was not effective when applied to normal prostate cells. The results describe a novel therapeutic model for the treatment of prostate cancer and provide support for future in vivo studies.

A molecular basis of cryopreservation failure and its modulation to improve cell survival

The requirement for more effective cryopreservation (CP) methodologies in support of the emerging fields of cell bioprocessing and cell therapy is now critical. Current CP strategies appropriately focus on minimizing the damaging actions of physicochemical stressors and membrane disruption associated with extra- and intracellular ice formation that occurs during the freeze-thaw process. CP protocols derived from this conceptual paradigm, however, yield suboptimal survival rates. We now provide the first report on the identification of delayed-onset cell death following CP and the significance of modulating molecular biological aspects of the cellular responses (apoptosis) to low temperature as an essential component to improve postthaw outcome. In this study we quantitatively examined the molecular basis of cell death associated with CP failure in a canine renal cell model. In addition, we report on the significant improvement in CP outcome through the modulation of these molecular mechanisms by the utilization of an organ preservation solution. HypoThermosol. Further, the utilization of HypoThermosol as the preservation medium and the modulation of molecular-based cell death have led to a paradigm shift in biologic preservation methodologies. The recognition of molecular mechanisms associated with CP-induced cell death offers the promise of improved CP of more complex and/or fragile biological systems such as stem cells, engineered tissues, and human organs.

The roles of iNOS in liver ischemia-reperfusion injury

To determine the contribution of the inducible nitric oxide synthase (iNOS) to hepatic injury following warm ischemia-reperfusion, we developed a model of partial hepatic ischemia-reperfusion in mice and studied the injury response in iNOS knockout (KO) mice. Compared with wild types, iNOS KO animals exhibited lower plasma transaminase levels after 1 and 6 h of reperfusion following 1 h of ischemia. At the 3-h time point, enzyme levels were not different between the two groups. iNOS mRNA was not detectable in the ischemic hepatic lobes of wild-type mice until 3 h of reperfusion; however, perfusion studies identified a significant delay in reperfusion of the ischemic lobe in the iNOS KO mice at the 1-h time point with similar perfusion rates at 3 and 6 h compared with wild type. By way of comparison, mice deficient in the endothelial NOS (eNOS) were also assessed for the degree of hepatic damage 3 h post-reperfusion. Plasma transaminase levels were significantly increased in eNOS KO animals compared with wild-type controls. These data suggest that systemic as well as local sources of iNOS regulate reperfusion, and local iNOS contributes to hepatic injury, while eNOS is protective in warm hepatic ischemia-reperfusion.

Chemo-cryo combination therapy: an adjunctive model for the treatment of prostate cancer

Despite continuing research and the development of alternate therapeutic options, prostate cancer remains problematic. Chemotherapy has played a minor role as a treatment option due to its lack of efficacy. Whereas cryotherapy has received renewed attention as a treatment modality, it too fails to offer an absolute curative option. Previously, we reported on the utilization of a therapeutic model, which, in combination, increases cell death in a canine renal cell model. Based upon that study, we investigated a combination therapy model as an alternative for the treatment modality for prostate cancer. We hypothesized that the combination of chemotherapy and cryosurgery would result in enhanced cell death, thereby presenting a more effective treatment of prostate cancer. A human prostate cancer cell (PC-3) model was exposed to 5-fluorouracil (5-FU) for 2 and 4 days (prefreeze), freezing (-5 to -100 degrees C), or a combination of the two treatments, and each was assessed for effectiveness over a 2-week posttreatment period. Additionally, investigation into the mechanisms of cell death initiated by the respective therapies was performed through DNA cleavage analysis. For chemotherapy, cultures exposed to 5-FU (2-4 days) yielded a 15-25% loss in cell survival. For cryotherapy, cultures exposed to a temperature window of -5 to -20 degrees C yielded an initial 5-70% loss of viability but cells propagated over time. Cultures exposed to temperatures of -25 to -80 degrees C yielded a 90-99% (+/-4.5%) initial loss in viability with repopulation observed by 12 days postthaw. Cells frozen to -100 degrees C yielded 100% (+/-0.3%) loss of viability and exhibited no signs of propagation. For chemo-cryo therapy, combination treatment at milder temperatures (-5 to -25 degrees C) resulted in an enhanced loss of cell viability compared to that for either treatment alone. Combination treatment at lower temperatures (-40 to -80 degrees C) resulted in a complete loss of cell viability. DNA fragmentation analysis at 48 h posttreatment revealed that dead (detached) cells treated with 5-FU died primarily through apoptosis, whereas dead cells from freezing (-15 degrees C) alone died primarily through freeze-rupture and necrosis. Detached cell analysis from combination treatment at -15 degrees C revealed the presence of apoptotic, necrotic, and freeze-rupture cell death. Scanning electron micrographs of cells exposed to freezing contributing to cell death. These data demonstrate that the combination of 5-FU at sublethal doses and freezing temperatures improves human prostate cancer cell death efficacy. Further, we suggest that chemo-cryo therapy offers a potential alternative treatment for the control and eradication of prostate cancer.

Characterization and cloning of a Tenebrio molitor hemolymph protein with sequence similarity to insect odorant-binding proteins

The yellow mealworm beetle, Tenebrio molitor, produces a number of moderately abundant low molecular weight hemolymph proteins ( approximately 12 kDa) which behave in a similar manner during purification and share antigenic epitopes. The cDNA sequence of the major component (THP12) was determined and the deduced protein sequence was found to be similar to those of insect odorant-binding proteins. Southern blot analysis suggests that at least some of the diversity in this family of proteins is encoded at the gene level. Both northern and western blot analysis indicate that THP12 is present in a variety of developmental stages and both sexes. THP12 was originally classified as an antifreeze protein, but the lack of antifreeze activity in the recombinant protein, as well as the clear separation of the antifreeze activity from THP12 following HPLC purification, has ruled out this function. The abundance of THP12, the similarity of THP12 to insect odorant-binding proteins, and the presence of hydrophobic cavities inside the protein (Rothemund et al., A new class of hexahelical insect proteins revealed as putative carriers of small hydrophobic ligands. Structure, 7 (1999) 1325-1332.) suggest that THP12 may function to carry non-water soluble compounds in the hemolymph. THP12 is also similar, particularly in structurally important regions, to other insect proteins from non-sensory tissues, suggesting the existence of a large family of carrier proteins which may perform diverse functions throughout the insect.

Cell viability improves following inhibition of cryopreservation-induced apoptosis

A new concept in cryopreservation solution design was developed that focuses on the use of an intracellular-type, hypothermic maintenance medium coupled with additives that inhibit cryopreservation-induced apoptosis. HypoThermosol' (HTS), a hypothermic (4 degrees C) maintenance medium utilized in the long-term storage of cell, tissue, and organ systems, was tested for cryoprotective capability on a renal cell line (Madin-Darby Canine Kidney cells). HTS and HTS derivatives were tested against conventional cell culture medium (Dulbecco's Minimal Essential medium, DME) as the cryoprotectant carrier solution because (1) cells are exposed to an extended state of hypothermia during the freeze-thaw process, and (2) HTS is designed to protect cells exposed to a hypothermic state. Cells separately cryopreserved in either HTS or DME + 5% dimethyl sulfoxide (DMSO) yielded equivalent 24-h postthaw survival (approximately 30%) and 5-d recovery (approximately 90%). Cells cryopreserved in CryoStor CS 5, a HTS derivative containing 5% DMSO, yielded approximately 75% 24-h postthaw survival and recovery to 100% within 3 d. DNA gel electrophoresis was performed to determine the mechanisms of cell death contributing to cryopreservation failure. Cells preserved in DME (DMSO-free) died primarily through necrosis, whereas cells preserved in either DME + 5% DMSO, HTS, or CryoStor CS 5 died through a combination of apoptosis and necrosis. This observation led to the inclusion of an apoptotic inhibitor designed to improve cryopreservation outcome. MDCK cells cryopreserved in CryoStor CS 5 supplemented with an apoptotic inhibitor (Caspase I Inhibitor V), hereafter termed CryoStor CS 5N, resulted in a 24-h postthaw survival and recovery rate exceeding that of any other cryoprotective solution tested (85%). We conclude that: (1) the use of HTS (a dextran-based, intracellular-type solution) without DMSO can yield postthaw viability equivalent to that of standard DMSO-based cryopreservation methods, (2) postthaw viability can be significantly increased through the use of an intracellular-type solution in conjunction with DMSO, (3) the use of HTS allows for cryopreservation to be accomplished with reduced levels of cryoprotectants, and (4) the regulation of apoptosis is essential for the improvement of cryopreservation outcome.

Cryosurgical effects on growing vessels

Cryosurgical treatment of unresectable hepatic malignancies has proven beneficial in adults. Concerns regarding its use in children include the effect on growth and the risk of injury to adjacent structures. To test the effect of cryoablation on adjacent vascular structures in a growing animal, liquid nitrogen cryoablation was performed on a juvenile murine model. Sprague Dawley rats underwent double freeze-thaw cryoablation of the abdominal aorta with interposed liver tissue. Serial sacrifices were performed over 120 days. Comparisons were made with sham-operated controls. Overall, animal growth paralleled that of sham controls through all time points. Gross examination of aortic diameter also showed similar growth in vessel size between the groups. Histologic analysis demonstrated injury after cryoablation with smooth muscle cell vacuolization, followed by cell death. Aortic media layer collapse resulted from cellular loss, however, elastin fiber composition was maintained. Aortic patency was preserved despite evidence of cellular injury and aortic wall remodeling. An associated thermal sink effect on the opposing wall was identified. After cryoablation adjacent to the abdominal aorta in adolescent rats, vascular patency is maintained and animal growth and structural function is preserved, despite cellular injury and wall compression. These observations suggest that cryoablation may be a useful treatment adjunct in young subjects.

Endoscopic cryotherapy: experimental results and first clinical use

BACKGROUND

Cryotherapy or the application of extreme cold has many potential applications in gastroenterology including tissue destruction and hemostasis but until now its development has been prevented by the lack of a delivery device suitable for use through the endoscope. We report here our experience with prototype devices using both liquid nitrogen driven by a cryosurgical system and cryogenic refrigerants (nitrous oxide and carbon dioxide) at or near ambient temperature.

METHODS

Cryotherapy was applied to the distal esophageal mucosa of dogs via a flexible catheter passed through an upper endoscope. In other dogs, cryotherapy was used for hemostasis in a bleeding ulcer model. The procedure was also used for palliation in a 58-year-old man with unresectable adenocarcinoma of the stomach with pyloric channel obstruction.

RESULTS

Freezing of the superficial mucosa was nearly instantaneous. All dogs survived the procedure and appeared to thrive. Histologic evaluation revealed significant necrosis of the superficial epithelial layer accompanied by a fibrinocellular infiltrate on the surface. These markers of acute injury subside by the fourth to sixth day and are replaced by regenerating epithelium, a process that is virtually complete by day 10. In the hemostasis experiments, bleeding ceased immediately after cryospraying of the lesions but resumed on thawing in most cases. Application of cryotherapy in the patient resulted in reduction of the pyloric mass with no immediately apparent adverse effects.

CONCLUSIONS

These data, although preliminary, demonstrate the feasibility of endoscopic cryotherapy using a simple hand-held device. This device has broad potential for use in gastroenterology including ablation of superficial epithelium, debulking of large tumors and hemostasis.

Mechanisms of tissue injury in cryosurgery

As the modern era of cryosurgery began in the mid 1960s, the basic features of cryosurgical technique were established as rapid freezing, slow thawing, and repetition of the freeze-thaw cycle. Since then, new applications of cryosurgery have caused numerous investigations on the mechanism of injury in cryosurgery with the intent to better define appropriate or optimal temperature-time dosimetry of the freeze-thaw cycles. A diversity of opinion has become evident on some aspects of technique, but the basic tenets of cryosurgery remain unchanged. All the parts of the freeze-thaw cycle can cause tissue injury. The cooling rate should be as fast as possible, but it is not as critical as other factors. The coldest tissue temperature is the prime factor in cell death and this should be -50 degreesC in neoplastic tissue. The optimal duration of freezing is not known, but prolonged freezing increases tissue destruction. The thawing rate is a prime destructive factor and it should be as slow as possible. Repetition of the freeze-thaw cycle is well known to be an important factor in effective therapy. A prime need in cryosurgical research is related to the periphery of the cryosurgical lesion where some cells die and others live. Adjunctive therapy should influence the fate of cells in this region and increase the efficacy of cryosurgical techniques.

Minimally invasive cryosurgery--technological advances

The technological advances which have caused renewed interest in cryosurgery are the development of intraoperative ultrasound to monitor the therapeutic process and the development of new cryosurgical equipment designed to use supercooled liquid nitrogen. The thin, highly efficient probes, available in several sizes, can be placed in diseased sites via endoscopy or percutaneously in minimally invasive procedures. The manner of use is to place the probe in the desired location in the diseased tissue with ultrasound guidance. If required by the size or location of the tumor, as many as five probes can be inserted and cooled to -195 degrees C simultaneously. The process of freezing is monitored by ultrasound which displays a hypoechoic (dark) image when the tissue if frozen. Rapid freezing, slow thawing, and repetition of the freeze/thaw cycle are standard features of technique. Clinical applications which have become common in the past 4 years include the treatment of prostatic cancer and liver tumors. The cases selected for cryosurgery are generally those for which no conventional treatment is possible. However, especially in prostatic cancer, the operative morbidity is so low and the results of therapy are sufficiently good in the short term to merit consideration of use in earlier stages of the disease. Diverse tumors in other sites, such as the brain, bronchus, bone, pancreas, kidney, and uterus, have also been treated in small numbers by cryosurgery. Judging from this experience, further expansion in the use of cryosurgical techniques seems certain.

Temperature Regulation of Supercooling and Gut Nucleation in Relation to Diapause of Pyrrhocoris apterus (L.) (Heteroptera)

The heteropteran Pyrrhocoris apterus (L.) does not survive freezing of its body fluids; there is a good correlation between values of survival at subzero temperatures and the supercooling point (SCP), i.e., the temperature at which body fluids start to freeze. The decrease of the SCP and thus the increase in cold hardiness is regulated by photoperiod and temperature. The relative importance of these factors depends on the physiological state of the insect. The SCP is about -7&deg;C at the onset of prediapause and a decrease of about 4-5&deg;C is associated with the development of the diapause syndrome in adults; these processes both are induced by a short-day photoperiod with temperature playing a secondary role. The induction of the diapause syndrome is a prerequisite for the subsequent decrease of the SCP by about 5-6&deg;C during cold acclimation. An intermediate temperature of 15&deg;C, or fluctuating outdoor temperatures and short-day photoperiods, are more suitable for the decrease of SCP than 5&deg;C in continuous darkness. The sensitivity to photoperiod gradually disappears during the development of diapause; after the termination of diapause around the winter solstice the SCP irreversibly increases at a high temperature of 26&deg;C even if exposed to a short-day photoperiod. The SCPs of hemolymph, gut, fat body, and gonads were compared to whole-body SCP. The gut was identified as the primary site of ice nucleation because its SCP value was very similar to the value for the whole body in both short-day and long-day insects. The SCPs of other organs, including the hemolymph, were always lower than the whole body SCP. Food was not a source of ice nucleating agents because the SCP of freshly ecdysed adults remained high after 2 weeks of starvation. In contrast, feeding was a prerequisite for the decrease of the SCP during prediapause. In postdiapause insects, the SCP increased at high temperatures in spite of the absence of food.

A comparative assessment of cryosurgical devices: application to prostatic disease

OBJECTIVES

To determine the comparative freezing ability of the Cryotech (CT) and AccuProbe (CMS) cryosurgical systems.

METHODS

Four conditions designed to model clinical situations were produced: (1) Single-probe performance in water at 17 degrees C; (2) five-probe performance in water at 17 degrees C; (3) single-probe performance in gel at 22 degrees C; and (4) single-probe performance in bovine liver. Parameters evaluated included temperatures at various time points (rates to and final low temperature), configuration of a freeze zone, and shaft freezing characteristics. In addition, isotherms were measured at predetermined distances from the center of the freeze zone.

RESULTS

Both systems provided freezing of various media under operational conditions. In water, the CMS 3-mm probe delivered more rapid freezing temperature rates than the 3-mm CT probe, with a 110 degrees C difference in probe surface temperature. In gel, the CMS probe increased freeze volume fourfold versus a twofold increase for the CT probe. In bovine liver, there was nearly equivalent performance with respect to geometry of the freeze ball. Extrapolation of the CT cooling curve indicated temperature equivalence at 30 minutes. A larger shaft diameter 4.9-mm CT probe produced results similar to the CMS probe in all the tested media. In addition, the freeze configuration of the CMS probe was spherical; the CT configuration was more cylindrical. CMS probe (equivalent diameter) tip temperatures were on average 100 degrees C lower.

CONCLUSIONS

Our tests demonstrated differences between the CMS and CT probe. The major differences are in the configuration of the freeze zone and shaft freezing. In equivalent conditions, the CMS 3-mm probe delivered more rapid cooling rates, a more spherical freeze ball, and lower absolute temperatures than the CT 3-mm probe. The larger CT probe produces equivalent freezing temperatures to the CMS probe, albeit with a more spherical shape. However, these in vitro systems may not adequately reflect varied prostate morphology. Further research is under way to determine if these differences affect relative efficacy of cryotherapy of the prostate.

A new solution for life without blood. Asanguineous low-flow perfusion of a whole-body perfusate during 3 hours of cardiac arrest and profound hypothermia

BACKGROUND

The benefits of hypothermia for preventing ischemic injury are well known, but its application in surgery to protect the whole body during procedures requiring circulatory arrest is currently limited to < 1 hour at 15 degrees C using 50% hemodilution. In a significant departure from previous methods, we have developed a technique of asanguineous blood substitution with low-flow perfusion and cardiac arrest at < 10 degrees C in a canine model. Our approach has been to design a hypothermic blood substitute that would protect the brain and visceral organs during several hours of bloodless perfusion. Two different solutions have been designed to fulfill separate requirements in the procedure.

METHODS AND RESULTS

With the use of extracorporeal cardiac bypass, 14 adult dogs were exsanguinated during cooling; 11 dogs were blood substituted using in combination the "purge" and "maintenance" solutions (group 1), and 3 dogs were perfused throughout with the "purge" solution alone as controls (group 2). After cardiac arrest, the solutions were continuously circulated for 3 1/2 hours by the extracorporeal pump (flow rate, 40 to 85 mL.kg-1.min-1; mean arterial blood pressure, 25 to 40 mm Hg). The temperature was maintained at < 10 degrees C (nadir, 6.6 +/- 0.1 degrees C) for 3 hours, and the hematocrit was kept at < 1% before controlled rewarming and autotransfusion. In the experimental group, the heart always started spontaneously in the temperature range of 11 degrees C to 27 degrees C, and 8 animals have survived long-term (current range, 14 to 110 weeks) without any detectable neurological deficit. In contrast, two control animals survived after extensive and aggressive cardiac resuscitation efforts; after surgery they exhibited transient motor and sensory deficits for approximately 1 week. Evaluation of biochemical and hematological parameters showed only a transient and inconsequential elevation in enzymes (eg, brain, liver, cardiac) in group 1 compared with the markedly greater elevations in group 2. For example, immediate postoperative values (mean +/- SEM) for lactate dehydrogenase were 114 +/- 10 for group 1 versus 490 +/- 210 for group 2 (P < .03); for SGOT, values were 93 +/- 18 for group 1 versus 734 +/- 540 for group 2 (P < .05). On day 1 for creatine kinase (CK), the group 1 value was 7841 +/- 2307 versus 71,550 +/- 2658 for group 2 (P = .03), and for CK-BB, the group 1 value was 108 +/- 22 versus 617 +/- 154 for group 2 (P = .03). Neurological evaluation using deficit scores (NDS) was based on a modification of the Glasgow Coma Scale score: 0, normal; 1, minimal abnormality; 2, weakness; 3, paralysis; 4, coma; and 5, death. At days 1 and 2 after surgery, NDS (mean +/- SEM) were 0 +/- 0 for the experimental group versus 1.5 +/- 0.5 for the control group. At days 3 and 7 after surgery, NDS were 0 +/- 0 for group 1 versus 1.0 +/- 1.0 for group 2.

CONCLUSIONS

The faster neurological recovery of dogs treated with the "intracellular-type" maintenance solution supports the biochemical data showing the benefits of this type of blood substitute for extending the safe limits of hypothermic cardiac arrest procedures to > 3 hours.

Development of a high-performance multiprobe cryosurgical device

The authors describe the design of the first multiprobe cryosurgical system (AccuProbe system). Compared with prior conventional cryosurgical devices, the new system has the following characteristics: 1) generation of subcooled liquid nitrogen, 2) optional use of up to five independently operated and controlled cryoprobes, 3) use of disposable probes of various sizes and shapes, 4) more accurate placement of the cryoprobes in the lesions due to probe miniaturization (3.4 mm in overall diameter), and 5) higher capacity freezing, which supports more accurate and controllable tissue temperatures. With the use of the newly developed system, numerous cryosurgical procedures, including those in the prostate, brain, and liver, have been successfully performed.

Transrectal ultrasound-guided percutaneous radical cryosurgical ablation of the prostate

BACKGROUND

The two major treatments for prostate cancer, radical prostatectomy and radiation therapy, are associated with considerable morbidity and variable results. This article presents the preliminary results using percutaneous radical cryosurgical ablation under ultrasound guidance to treat prostate cancer.

METHODS

The patient group consisted of all patients with localized prostate cancer who underwent cryosurgery between June 1, 1990 and May 1, 1992. Patients in Group 1 were treated by freezing of the tumor with two cryoprobes placed multiple times. Group 2 patients were treated by freezing of the tumor with five cryoprobes placed simultaneously. Cryoprobes (3 mm in diameter) were placed percutaneously with a transperineal approach. Cryoprobe placement and freezing were monitored using the transrectal ultrasound.

RESULTS

Of the 55 patients (68 procedures) undergoing treatment, 23 have 3 months of follow-up with associated biopsy (Group 1, 8 patients; Group 2, 15 patients). In Group 1, three (37.5%) patients had residual disease. In Group 2, one (6.7%) patient had residual disease, whereas 14 (93.3%) patients did not. Combining both groups, 19 (82.6%) patients had no residual disease, whereas 4 (17.4%) patients had positive results on postoperative biopsy. Complications included rectal freezing, urethrorectal fistula, sloughing urethral tissue, impotence, perineal ecchymosis, penile edema, and ileus.

CONCLUSIONS

Preliminary results indicate that percutaneous transperineal ultrasound-guided prostate cryosurgery may be an effective treatment for prostate cancer with minimal associated morbidity.

Extracellular calcium does not contribute to cryopreservation-induced cytotoxicity

The possible role of extracellular calcium ([Ca+2]e) in cryopreservation-induced cytotoxicity was tested using Madin-Darby canine kidney (MDCK) cells and a fluorescent multiple endpoint assay. MDCK cells maintained in 2 mM [Ca+2]e and treated with the calcium ionophore, ionomycin, increased their intracellular calcium ([Ca+2]i) as revealed by the calcium indicator dye, Fluo3 and the bottom-reading spectrofluorometer, CytoFluor 2300. The addition of 10 mM [ethylene bis (oxyethylenenitrilo)]-tetraacetic acid (EGTA) to the extracellular medium before treatment with ionomycin blocked this ionomycin-dependent increase in [Ca+2]i. A number of site and activity-specific fluorescent probes were surveyed to determine which indicator dye might best reveal the ionomycin-induced cytotoxic events during this increase in [Ca+2]i. Although most dyes changed their emission profiles in response to calcium, neutral red was found to best reflect the loss of [Ca+2]i homeostasis. The NR50 for a 15-min exposure to ionomycin in the presence of 2 mM [Ca+2]e was approximately 2 microM ionomycin, but ionomycin had little apparent effect on neutral red retention when 10 mM EGTA was added to the extracellular medium. Thus it was clear that an increase in [Ca+2]i could be cytotoxic to MDCK cells and that neutral red could monitor this cytotoxic episode. To test if [Ca+2]e was similarly cytotoxic during cryopreservation, MDCK cells were subjected to cryopreservation in the presence of dimethylsulfoxide (DMSO). In contrast to previous studies, plasma membrane integrity, not lysosomal function, seemed to best correlate with cell survival subsequent to cryopreservation. In addition, decreasing [Ca+2]e had no discernable effect on the retention of plasma membrane indicator dyes, neutral red, or cell survival. It is concluded that a) plasma membrane indicator dyes, not neutral red, might be better indicators of cytotoxicity occurring during cryopreservation; b) DMSO might be toxic to lysosomes during cryopreservation of cultured cells; and c) although [Ca+2]e can contribute to cytotoxicity, the presence of [Ca+2]e might not influence cryopreservation-induced cytotoxicity.

Biochemical modification of plasma ice nucleating activity in a freeze-tolerant frog

Recently, we reported the presence of ice nucleating activity, apparently proteinaceous, in the plasma of a freeze-tolerant frog, Rana sylvatica, collected in autumn and spring. Although this protein has not been purified, its ice nucleating behavior can act as an internal reference for tests that attempt to modify its ability to nucleate ice formation. If the addition of a chemical reagent alters the temperature of ice crystallization compared with the control, it can be assumed that protein modification may have occurred. The ice nucleating protein in R. sylvatica showed resistance to proteolysis with four different proteases although there was a significant reduction in the temperatures of nucleation with these treatments (ANOVA P less than 0.001). However, ice nucleating activity was lost when plasma was treated with the addition of urea or N-bromosuccinimide. Modification of protein sulphydryl groups with iodoacetamide did not affect the crystallization temperature (Tc) but treatment with iodoacetic acid resulted in a significant increase in Tc of plasma. An abrupt loss of ice nucleating ability was observed in plasma samples after heating above 87 degrees C. Anomalous potentiation of ice nucleating activity occurred when the plasma was heated to and held at temperatures between 67-75 degrees C.

Calorimetric analysis of antifreeze glycoproteins of the polar fish, Dissostichus mawsoni

Solutions of antifreeze glycoproteins 1 through 5 and 8 were analyzed for activity by differential scanning calorimetry. With a scan rate of 1 degree C min-1, antifreeze glycoproteins 1-5 (20 mg/ml) revealed antifreeze activity with a delay in the freeze exotherm during cooling in the presence of ice. Antifreeze glycoprotein 8 (60 mg/ml), however, did not reveal antifreeze activity. When a 0.1 degree C min-1 scan rate was used, glycoproteins 1-5 again yielded a delay in the freeze onset, but the exotherm consisted of multiple events. At the slower scan glycoprotein 8 revealed an initial freeze followed by multiple exothermic events resembling those of glycoproteins 1-5. Thermograms exhibiting antifreeze activity had an initial shoulder in the exotherm direction upon cooling followed by a delay before the exotherm. The shoulders were correlated with c-axis ice growth observed in visual methods. The glycoprotein antifreezes had a linear increase in activity with decreased ice content.

Ultra-rapid freezing by spraying/plunging: pre-cooling in the cold gaseous layer

A thermophysical model is established to analyse the influence of pre-cooling of a biological specimen in the cold gas layer associated with spray-freezing techniques. The basic principles governing the process of pre-cooling are provided. It is concluded that pre-cooling is one of the major limiting steps in attaining an overall ultra-rapid cooling rate. Pre-cooling has a substantial influence on the nature of the final frozen specimens. In order completely to avoid crystallization before entry into the liquid cryogen and maximize the overall cooling rate of the specimen, precautions should be taken to control the height of the gaseous layer and the size of the specimen. The probability of the specimen being frozen in the cold gaseous layer is reduced by increasing the entry speed. The effectiveness, however, becomes less marked at speeds greater than 10 m s. In order to minimize the risk of misinterpreting the measured cooling rate, it is necessary to specify the pre-cooling conditions. The pre-cooling effect is much more evident in liquid helium than in cryogens such as propane, ethane, Freon 12, 13 and 22.

Physical aging of glassy state: DSC study of vitrified glycerol systems

After annealing during the glass transition temperature (Tg) range or at sub-Tg temperatures, a "Tg overshoot" has been observed by differential scanning calorimetry in vitrified 55 and 80% (W/W) glycerol solutions. The temperature dependence of the overshoot is most pronounced immediately below the Tg and always increases in amplitude with lengthened annealing periods, whether annealed during Tg range or below. Of particular note is the anomalous shift in devitrification temperature (Td) to lower temperatures following increased time of annealing at sub-Tg temperatures. The Tg obtained on warming also occurs at higher temperatures with increased annealing times. The results allow us to suggest the existence of the time and temperature dependency of the glassy state. Accordingly, it may be desirable to maintain vitrified biological systems at temperatures sufficiently below Tg so that the extent of relaxation in the glass system is avoided or minimized during cryopreservation. The relaxation effects must be taken into account prior to warming a biological system after a long-term cryopreservation. These effects should also be considered in studies of vitrification solutions.

Vitreous domains in an aqueous ribose solution

Aqueous solutions containing d-ribose demonstrate the ability to form more than one vitreous domain when exposed to low temperatures. Differential scanning calorimetry revealed two glass transitions (at Tgs of -63 and -43 degrees C) upon cooling and warming at a constant rate of 5 degrees C.min-1. The bulk water of the solution crystallizes at -18 degrees C (Tc). Heat capacity and enthalpy changes, and the derivatives for each thermal event, are calculated. Relaxation studies on the observed Tgs produced anticipated overshoots characteristic of the presence of glassy states.

Ice nucleating activity in the blood of the freeze-tolerant frog, Rana sylvatica

Although the presence of antifreeze and ice nucleating agents in the hemolymph of insects has been well documented, there have been no reports of either of these types of agent in vertebrates. The technique of differential scanning calorimetry was used to examine the blood, serum, and plasma of a freeze-tolerant frog, Rana sylvatica, for the presence of antifreeze protein activity. Results demonstrate the absence of antifreeze protein but the presence of an ice nucleating agent that may serve as a functional component of the overwintering strategy of this species. Ice nucleating activity was detected in samples of cell-free blood, serum, and plasma, suggesting that the agent is a soluble component and possibly plasma protein. To our knowledge, the identification of ice nucleating activity in this freeze-tolerant vertebrate is novel.

Effect of cooling rate on the survival of larvae, pupariation, and adult emergence of the gallfly Eurosta solidaginis

Freeze-tolerant third instar larvae of the gallfly Eurosta solidaginis were cooled at 10, 5, 1, and 0.1 degrees C min-1 to -40 degrees C and then warmed to +5 degrees C at 1 degree C min-1. After cooling and warming the larvae were transferred to 21 degrees C and the survival of larvae, success of pupariation, and adult emergence were monitored at daily intervals in comparison to an uncooled control sample. The percentage emergences of flies from larvae cooled at 10, 5, 1, and 0.1 degree C min-1 and in the control were 7, 13, 37, 77, and 67%, respectively. A number of flies in each group emerged with malformed (unextended) wings and an unretracted ptilinum on the head capsule. The percentage emergences of normal flies at the four cooling rates and from the control were 3, 0, 17, 47, and 57%. At 48 hr after exposure all larvae in each treatment were alive. First mortality was observed between 48 and 72 hr after cooling and increased with time at each cooling rate. Mortality was apportioned into four phases of development: larva, pupariation, and early and late pupae. Mortality commenced earlier at the faster cooling rates; at 10 degrees C min-1, 37% of the sample died as larvae and a further 20% failed to complete pupariation, whereas at 0.1 degree C min-1, only 3% died as larvae and 97% formed a puparium.

Differential scanning calorimetric analysis of antifreeze protein activity in the common mealworm, Tenebrio molitor

Antifreeze proteins (AFP) are able to inhibit the growth of ice-crystals at temperatures below the equilibrium freezing point (Tf) of hemolymph. The analysis of AFP activity has commonly involved the use of direct microscopic observation of a sample following inoculation with ice. The resulting activity, defined as the amount of thermal hysteresis observed between Tf and the subsequent rapid growth of ice, has been reported to range up to 7 degrees C. However, most studies report high level of variation, possibly due to ice-crystal size variability and the presence of non-visible ice nuclei. We describe a new method of analysis of AFP activity using differential scanning calorimetry (DSC). DSC analysis reveals much higher activity, up to 10 degrees C, with less variation observed within a sample, and is not subject to the difficulty of accurate assessment of ice-crystal volume.

Fecundity and longevity of houseflies after space flight

After 7 days of space flight house flies, Musca domestica, exhibited similar longevity, but a reduction in reproductive output as compared to earthbound controls. This reduction was not observed in later generations. These data suggest that space flight directly alters the rate of ovarian development, but that this effect is not genetically transmitted.

Protective agents: regulation of synthesis

The exogenous cues to overwintering adaptations vary not just between components of hardening but between species. One species, P. brevicornis, initiates glycerol synthesis in response to 0 degree C exposures while a second species, E. solidaginis, increases glycerol levels not in response to temperature but in apparent association with changes in total body mass. This species maintains a constant annual percentage of water while occupying a hibernaculum that dries considerably. During overwintering, E. solidaginis losses approximately 50% of its total body mass. In addition to the changes described, this species (northern populations) increases the amount of water bound to both protein and low-molecular-weight compounds during hardening. The increase in binding exceeds threefold between 25 and -30 degrees C (0.193 to 0.633 g/g dry wt) (29). These data do not unequivocally demonstrate the existence of a hydration trigger to glycerol synthesis but are adequate to put forth such a hypothesis. A decrease in total bulk water levels due to both wet weight loss and increases in bound water may provide conditions of functionally reduced intracellular metabolic water. Since polyol production necessitates the disruption of carbon flow between glucose-6-phosphate and pyruvate, one or more enzymes may be sensitive to water reductions. Pyruvate kinase is sensitive to available water levels. Inhibition of this enzyme would likely cause a shunting of carbon metabolism to glycerol production. This hypothesis becomes attractive in light of the observation that in a variety of species, glycerol accumulations have been correlated with dehydration and hyperosmotic conditions. A common adaptative mechanism may exist in response to apparently different environmental perturbations.

Time course of peripheral heterothermy in a homeotherm

The integrity of the peripheral heterothermic response was monitored in adult Sprague-Dawley rats during cold acclimation. Subcutaneous peripheral temperature gradients were simultaneously recorded in the hindlimbs. One limb was exposed to room temperature (22 +/- 2 degrees C) while the contralateral limb was gradually cooled to 0 +/- 1 degrees C. Noncontrols were acclimated at 5 +/- 1 degrees C for periods up to 35 days. Controls responded to the cooling regimen (25 to 0 degrees C at 0.5 degrees C . min-1) in a "poikilothermic" manner indicating local cold-induced vasoconstriction (CIVC). CIVC was not released until tissue temperatures reached 22,3 +/- 2.5 degrees C whereupon nonpatterned limb temperature fluctuations, Lewis' hunting response, were often initiated. The hunting response occurred synchronously in the contralateral warmed limb despite its elevated temperature. The experiments revealed a progressive decrease in the intensity of heterothermy indicative of an earlier onset of cold-induced vasodilation as well as increased resistance to tissue cooling with increasing acclimation time. Following 21 days at 5 degrees C, limb exposure to 0 degrees C resulted in a 2-4 degrees C drop in tissue temperature. The time course of the diminution in peripheral heterothermy is discussed. In addition, evidence supporting the hypothesis of a central component in the regulation of the hunting response is presented.