Decreased insulin binding to porcine adipocytes in vitro by beta-adrenergic agonists

The present study was conducted to determine the influence of dibutyryl-cAMP (dbcAMP), epinephrine, ractopamine and clenbuterol on insulin binding to porcine adipocytes. Dibutyryl-cAMP decreased insulin binding to swine adipocytes by 40 and 20% at 1.8 and 25.8 ng insulin/ml, respectively. Ractopamine and clenbuterol directly reduced insulin binding at the low insulin concentration and decreased binding at high insulin concentrations in the presence of adenosine deaminase. Scatchard analysis suggested that the reduction of insulin binding was due to a decrease in receptor number. Epinephrine alone did not influence insulin binding. In the presence of theophylline, epinephrine decreased binding at both low and high insulin concentrations; however, ractopamine plus theophylline decreased binding only at the low insulin concentration. Clenbuterol did not affect insulin binding in the presence of theophylline. Propranolol blocked the inhibitory effect of epinephrine on insulin binding. These beta-adrenergic agonists can inhibit insulin binding and, thus, antagonize insulin action in swine adipocytes.

Beta-tubulin epitope expression in normal and malignant epithelial cells

The expression of a unique beta-tubulin isoform (class III) was monitored in squamous cell carcinoma (SCC) and normal epithelial cells using a monoclonal tubulin antibody called TuJ1. Whole tissue homogenates of SCC, normal tissue, SCC grown in nude mice, and SCC cultured cells were examined using sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot. TuJ1 antibody localization was performed using peroxidase immunostaining on paraffin sections of SCC, normal tissue, nude mouse SCC, and immunofluorescent microscopy of SCC cultured cells. The malignant tissues examined stained positive with TuJ1 and a general beta-tubulin antibody, whereas the normal tissues stained positively only for the general beta-tubulin antibody. TuJ1 epitope expression may be a useful marker for SCCs and may assist in understanding differences between normal and malignant squamous cells.

Effects of ractopamine on adipose tissue metabolism and insulin binding in finishing hogs. Interaction with genotype and slaughter weight

Twenty-four barrows were divided among eight treatments in a 2 x 2 x 2 design to quantify the influence of ractopamine (0 or 20 mg/kg diet) over the final 40 kg of gain on metabolic activity in adipose tissue. Interactions with genotype (Hampshire cross or Landrace cross) and slaughter weight (100 or 127 kg) were investigated also. Backfat was removed at slaughter and rates of lipolysis and fatty acid synthesis (FS), activities of malic enzyme (ME) and fatty acid synthetase (FAS), and insulin binding to adipocytes were assessed. Adipocytes from ractopamine-fed pigs were less sensitive (EC50 increased 90%) and had a lower maximum lipolytic response (40%) to ractopamine stimulation. Rates of basal and insulin-stimulated FS were decreased 40% in ractopamine-fed pigs and were reflected in lower activities of ME (50%) and FAS (15%). Breed and slaughter weight had no consistent influence on the ractopamine response. Landrace-cross pigs had greater insulin binding capacity (30-60%) whether data were expressed on a cell or surface area basis. Ractopamine feeding did not consistently affect insulin binding capacity. Results suggest that ractopamine interacts in vivo with the beta-adrenergic receptor of swine adipocytes, decreasing lipogenic capacity and diminishing responsiveness to beta-adrenergic stimulation.

Carcinoma arising in oncocytic Schneiderian papilloma

Two men aged 54 and 73 years, respectively, had oncocytic Schneiderian papilloma (OSP) containing synchronous carcinoma at the time of first biopsy. In both cases, invasive carcinoma involved a small proportion of excised tissue and was in continuity with dysplastic surface epithelium. Our cases document that the epithelial component of OSP can undergo malignant transformation. The focal involvement of OSP with carcinoma underscores the need to examine all excised tissue microscopically.

Sensitivity of lipolysis and lipogenesis to dibutyryl-cAMP and beta-adrenergic agonists in swine adipocytes in vitro

The sensitivities of lipolysis and fatty acid synthesis to dibutyryl-cAMP (dbcAMP), epinephrine, ractopamine and clenbuterol were quantified in vitro using porcine adipocytes. Insulin-stimulated lipogenesis showed a biphasic response to dbcAMP, with increased rates at low concentrations and decreased (55%) rates at higher concentrations of dbcAMP. In the absence of insulin, lipogenesis was inhibited 78% by dbcAMP. In the presence of adenosine deaminase or theophylline, all three beta-adrenergic agonists inhibited basal lipogenesis, but only epinephrine and ractopamine inhibited insulin-stimulated lipogenesis. The relationship between suppressed lipogenesis and enhanced lipolysis in response to dbcAMP and the beta-agonists revealed that 1) basal lipogenesis was more sensitive to inhibition than was the stimulation of lipolysis, 2) sensitivity differences were magnified if adenosine deaminase was present and 3) insulin decreased adipocyte sensitivity to the inhibitory effects of dbcAMP and the beta-adrenergic agonists. These results indicate that the relative sensitivities of lipogenesis and lipolysis to beta-adrenergic stimulation can be modified by adenosine and insulin. Furthermore, adenosine and insulin antagonize beta-adrenergic responses, in part, by cAMP-independent mechanisms.

Clear cell tumor of the lung. A clinicopathologic, immunohistochemical, and ultrastructural study of eight cases

We studied eight clear cell tumors of the lung (CCTL) to better define their clinical, immunohistochemical, and ultrastructural features, and to clarify their distinction from other neoplasms, particularly metastatic renal cell carcinoma. Patients ranged in age from 31 to 67 years (mean, 51 years). Seven patients had clinically benign, asymptomatic lesions measuring less than 2 cm in diameter that were devoid of necrosis. The eighth patient had a symptomatic, partially necrotic CCTL 4.5 cm in diameter that metastasized to the liver and peritoneum; the patient died of tumor 17 years after diagnosis. Ultrastructural study of seven CCTL showed interdigitating cell processes (all cases), primitive cell junctions (five of seven cases), intracytoplasmic glycogen (all cases), and rare dense core granules (two of seven cases). Immunohistochemically, paraffin-embedded sections from all eight CCTL were negative for cytokeratin (CK), epithelial membrane antigen (EMA), chromogranin, and vimentin. Focal staining was seen for S-100 protein (three of eight cases), neuron-specific enolase (three cases), synaptophysin (one case), and Leu 7 (one case). Although these findings suggest that at least some CCTL exhibit neuroendocrine differentiation, the tumor's histogenesis remains uncertain. Of more practical importance, the combined absence of CK, EMA, and vimentin in formalin-fixed, paraffin-embedded CCTL virtually precludes confusion with renal cell carcinoma. Although traditionally considered benign, CCTL larger than 2 cm that are symptomatic, and focally necrotic should be regarded as potentially malignant neoplasms.

Insulin binding to mouse adipocytes exposed to clenbuterol and ractopamine in vitro and in vivo

Insulin binding to mouse adipocytes was measured after in vitro (30 min) and in vivo (5 days) exposure to clenbuterol and ractopamine. At 10(-6) M, both agonists decreased insulin binding by 20-30% after a 30 min preincubation at each insulin concentration between 1 and 25 ng/ml. Binding was not decreased if propranolol was present. Scatchard plots suggested that decreased binding was due to a decrease in insulin receptor concentration. Insulin binding was decreased approximately 10% at agonist concentrations as low as 10(-13) M, but binding was not further decreased until concentrations exceeded 10(-9) M. Rate of gain was increased 2-fold by clenbuterol (10 mg/liter of drinking water) and 50% by 500 mg ractopamine/liter, but not by 50 mg ractopamine/liter. Clenbuterol and ractopamine (500 mg/liter) decreased fat pad weight but only clenbuterol increased hind limb muscle mass. Insulin binding following in vivo administration was not influenced by ractopamine at 50 mg/liter, but tended to be increased by clenbuterol and ractopamine at 500 mg/liter. The disparity in results between administering the beta-agonists in vitro or in vivo suggests that counter regulatory factors influenced insulin binding capacity in vivo. Results indicate that ractopamine and clenbuterol can decrease insulin binding to adipocytes but the relevance of this response to decreased fat accretion is not clear.

Determination of the affinity of ractopamine and clenbuterol for the beta-adrenoceptor of the porcine adipocyte

Dissociation constants (Kd) of ractopamine and clenbuterol for the swine adipocyte beta-adrenergic receptor were estimated from competition studies with epinephrine for the stimulation of lipolysis. Both compounds competitively inhibited epinephrine-stimulated lipolysis in the absence of adenosine deaminase. Three methods for estimating Kd values were used and similar estimates were obtained with each method. Ractopamine and clenbuterol showed greater affinity for the beta-receptor than did epinephrine and had similar Kd values of 1 to 2 x 10(-7) M. The low capacity of ractopamine and clenbuterol to stimulate lipolysis in vitro does not result from poor coupling to the beta-receptor. Ractopamine and clenbuterol may be considered partial agonists, possessing high affinity for the beta-adrenoceptor but exhibiting a relative ineffectiveness for adenylate cyclase activation.

Adipose tissue lipogenesis in growing steers adapted to different levels of feed intake

The association between feed intake and lipogenic activity in adipose tissue was investigated in growing cattle. Twenty-five 300-kg steers were allotted by BW to one of five levels of intake of a single high-energy corn-corn silage-based diet. Steers were adapted to diets over 4 wk and intakes were adjusted weekly to achieve steady but varying rates of growth. Daily intakes (% of BW) averaged .92, 1.15, 1.64, 2.28 and 2.69 and resulted in growth rates over the final 3 wk of -.28, .07, .71, 1.67 and 1.69 kg/d, respectively. Lipogenic activities in biopsied tissue and circulating concentrations of glucose and insulin were lowest at maintenance feeding and below but increased linearly (P less than .01 for lipogenesis; P less than .1 for glucose and insulin) as intake increased above maintenance. Mean minimal and maximal rates (mumoles.-min(-1).10(6) cells(-1)) or concentrations were fatty acids synthesis ([14C]acetate---fatty acid)), .065 and .723; fatty acid synthetase (NADPH oxidized), .266 and 2.97; lipoprotein lipase (fatty acid released), .048 and .359; glucose (mg/dl), 60.4 and 70.7 and insulin (ng/ml), .70 and 1.66. In a preliminary study with the same 25 steers fed ad libitum, nearly 25% of the variability in adipose tissue lipogenesis was accounted for by variation in feed intake. Results indicate that activities of lipogenic enzymes and lipogenic capacity in growing steers coordinately adapt to the level of feed consumed and that nutrient availability and(or) insulin concentrations may participate in this adaptation.

Effect of suppression of prolactin secretion on adipose lipogenesis in the postpartum beef cow

Effects of inhibiting prolactin secretion and of calf removal at 3 d postpartum on the lipogenic capacity of s.c. adipose tissue were investigated in postpartum beef cows. The rate of fatty acid synthesis (SYN) from [1-14C]acetate and the activity of fatty acid synthetase (FAS) were assessed on adipose tissue obtained by biopsy at 1, 2, 4, 8 and 10 wk postpartum. Administration of bromocriptine (BR; a drug that suppresses prolactin secretion in rats) between d 7 and 42 postpartum decreased average serum prolactin concentrations nearly 90%, but BR had no effect on lipogenic rates at any week compared to control (CO) cows. Rates of SYN (nmol acetate.min-1.g-1 tissue) increased linearly in CO and BR cows from a nadir of 3.1 at wk 1 to 19.3 by wk 8. Within CO and BR, cows with the greater energy intake relative to requirements for lactation (energy balance) had the faster rates of recovery of SYN. Cows whose calves were weaned early (3 d) showed rapid early increases in SYN, reaching an average maximum rate of 46.2 by wk 2. Activity of FAS generally followed a pattern similar to that of SYN for all groups. Results indicate that prolactin is not responsible for low rates of postpartum lipogenesis in s.c. adipose tissue and that energy intake influences the rate of recovery.

Acute effects of beta-adrenergic agonists on porcine adipocyte metabolism in vitro

Backfat was obtained at slaughter from market weight hogs to study the acute effects of clenbuterol (CB), ractopamine (RAC) or epinephrine (EPI), in the presence and absence of theophylline (THEO) or adenosine deaminase (ADA), on rates of lipolysis and fatty acid synthesis in vitro. Only EPI increased lipolytic rate in the absence of THEO or ADA. In the presence of THEO or ADA, RAC and CB were lipolytic, although CB had a lower maximal response. With THEO present, RAC and EPI increased lipolysis with a similar potency and responsiveness. Lipolytic responses from all agonists were prevented by propranolol. Insulin stimulated glucose incorporation into fatty acids 50 to 100%; stimulated rates were not influenced by any agonist, either alone or in the presence of ADA. When THEO was present, EPI and RAC inhibited fatty acid synthesis approximately 50%. Clenbuterol was not inhibitory under any conditions. Results indicate that, under appropriate conditions, beta-adrenergic agents increase lipolysis and decrease lipogenesis in porcine adipocytes. Combined evidence suggests that lipolysis is more sensitive to beta-adrenergic stimulation than is insulin-stimulated lipogenesis. Finally, RAC and CB possess only partial agonist activity relative to EPI, CB being least active.

The presence and estrogen control of immunoreactive calbindin-D9k in the fallopian tube of the rat

The present study was undertaken to localize and investigate the endocrine control of immunoreactive 9K calbindin-D9k in the fallopian tube (oviduct) of the rat. Rat fallopian tubes were excised with the uterus, immediately fixed by freeze-substitution, and processed for immunoperoxidase staining. Staining employed a rabbit antiserum against purified rat intestinal calbindin-D9k and the streptavidin-biotin technique. Calbindin-D9k immunoreactivity was localized to luminal epithelial cells of the fallopian tube of mature rats, with no staining observed in other tissue layers of the tube. Epithelial cells in both the isthmus and the ampulla were positive for calbindin-D9k. In weanling rats, which have little ovarian function but high levels of 1,25-dihydroxyvitamin D, no immunoreactive calbindin-D9k was observed in any part of the tube. However, after daily injections of estradiol (6 micrograms/day) for 3 days, intense staining was observed in the epithelial cells of the immature rat fallopian tube. Progesterone treatment (1 mg/day for 3 days) of immature rats had no effect on calbindin-D9k in fallopian tube. The lumen of the fallopian tube (oviduct) is the key location for fertilization, a process that requires a narrowly defined concentration of extracellular calcium. By analogy to the intestine, calbindin-D9k may play a role in the transcellular movement of calcium across the fallopian tube epithelium in the fallopian tube lumen.

"Undifferentiated" neoplasms of the sinonasal region: differential diagnosis based on clinical, light microscopic, immunohistochemical, and ultrastructural features

Sinonasal neoplasms and neoplasm-like proliferations composed of light microscopically poorly differentiated or undifferentiated, small- to medium-sized cells cause considerable diagnostic confusion. Lesions in this category include lymphoepithelioma (undifferentiated carcinoma), olfactory neuroblastoma, small-cell undifferentiated (oat cell) carcinoma, sinonasal undifferentiated carcinoma, malignant melanoma, pituitary adenoma, lymphoid hyperplasia, malignant lymphoma, plasmacytoma, lymphomatoid granulomatosis, rhabdomyosarcoma, mesenchymal chondrosarcoma, small cell osteosarcoma, Ewing's sarcoma, and synovial sarcoma. Many of these lesions can be definitively diagnosed based on light microscopic features alone, but, in some instances, additional techniques such as immunohistochemistry are of value. The authors review the pertinent clinicopathologic features of the above lesions, with emphasis on light microscopic, immunohistochemical, and ultrastructural features of particular utility in differential diagnosis.

Vascular adrenal cysts. A clinicopathologic and immunohistochemical study of endothelial and hemorrhagic (pseudocystic) variants

Three endothelial cysts and five hemorrhagic cysts (pseudocysts) arose in the adrenal glands of seven patients aged 23-73 years. Four patients were male and three were female. Five were symptomatic and gave abdominal pain as their chief complaint. Endothelial cysts were collapsed or filled with serous fluid, multiloculated, had an endothelial lining, and often contained adrenal cortex in their outer walls. The endothelial lining reacted only weakly for Factor VIII-related antigen (FVII-RAg), but it stained strongly for collagen type IV (C-IV). The lack of hemorrhage and the FVIII-RAg/C-IV staining pattern in endothelial cysts suggest lymphatic differentiation. Hemorrhagic cysts were spherical, firm masses containing clotted blood and hyalinized thrombus with attenuated adrenal cortex in the outer fibrous wall. Islands of intact cortical cells were present deep within the thrombi of four hemorrhagic cysts. Three of five hemorrhagic cysts stained strongly for FVIII-RAg and C-IV in irregular vascular channels of the attenuated cortex and within the cyst contents. These channels suggest that at least some hemorrhagic cysts arise when hemorrhage occurs in a preexisting blood vascular anomaly. Entrapment of cortical islands by extravasated blood in hemorrhagic cysts may be misdiagnosed as necrotic cortical neoplasm. To avoid confusion, one must recognize the normality of the entrapped cortical cells, identify an intrinsic vascular anomaly, and distinguish thrombus from necrotic tumor.

Serous papillary carcinomas arising from the peritoneum and ovaries. A clinicopathologic and immunohistochemical comparison

Primary papillary serous carcinoma arising from the peritoneal surface (serous surface papillary carcinoma; SSPC) is a distinctive neoplasm with a histomorphologic resemblance to serous ovarian papillary carcinoma (SOPC). To determine if these tumors are similar antigenically, we studied 13 examples of SSPC and 31 of SOPC immunohistochemically. Antibodies to several determinants known to occur in the Müllerian epithelium were employed. Both neoplasms were uniformly positive for cytokeratin and epithelial membrane antigen (EMA); in addition, SSPC and SOPC were similar in quantitative and qualitative reactivity for B72.3 antigen, carcinoembryonic antigen, Leu M1, CA-125 antigen, LN1, LN2, MB2, S100 protein, placental alkaline phosphatase, and amylase. Residual nonneoplastic mesothelium failed to express any of these antigens except for cytokeratin, EMA, and CA-125. The clinical behavior of SSPC was similar to that of high-stage SOPC; all patients with adequate follow-up died of their tumors. These results suggest that SSPC and SOPC are analogous lesions, with respect to their cellular differentiation. Moreover, it would appear that both neoplasms display only a limited immunophenotypic homology to the mesothelium.

Analysis of lymphoepithelioma and lymphoepithelioma-like carcinomas for Epstein-Barr viral genomes by in situ hybridization

Lymphoepithelioma of the nasopharynx has a strong association with Epstein-Barr virus (EBV). To test the hypothesis that lymphoepithelioma-like carcinomas occurring at other sites are also associated with EBV virus, we used in situ hybridization to analyze 20 cases of lymphoepithelioma and histologically similar lesions and five basaloid squamous cell carcinomas for evidence of EBV genomes. EBV genomes were demonstrated in six of six lymphoepitheliomas of the nasopharynx but in none of five basaloid squamous cell carcinoma. Only one of 14 lymphoepithelioma-like carcinomas was found to contain EBV genomes. The single positive lymphoepithelioma-like carcinoma occurred in the lung of an Asian patient, suggesting that ethnic or geographic influences may be important in determining whether EBV is associated with these nonnasopharyngeal neoplasms. Despite their histologic similarity, most lymphoepithelioma-like carcinomas probably have a different pathogenesis from nasopharyngeal lymphoepithelioma.

Peritoneal malignant mesothelioma versus serous papillary adenocarcinoma. A histochemical and immunohistochemical comparison

In order to evaluate adjunctive histologic methods for separating mesothelioma (MM) and serous adenocarcinoma (SC), we studied 28 and 46 respective cases histochemically and immunohistochemically. Ten serous adenocarcinomas arose primarily in extraovarian sites within the abdomen. Diagnoses in each case were established retrospectively by a combination of electron microscopy and clinicopathologic correlation. A panel of antibodies to cytokeratin (CK), epithelial membrane antigen (EMA), B72.3, placental alkaline phosphatase (PLAP), S-100 protein, carcinoembryonic antigen (CEA), Leu M1, CA-125, and amylase (AM) was applied to paraffin sections of each case. Serous carcinoma was reactive for neutral mucins whereas mesothelioma was not; however, only 50% of adenocarcinoma cases stained in this manner. Peritoneal mesothelioma showed reactivity for CK (28 of 28 cases), EMA (24 of 28 cases), AM (five of 28 cases), CA-125 (four of 28 cases), and S-100 protein (three of 28 cases), but lacked B72.3, PLAP, and CEA. Three mesotheliomas expressed Leu M1, but in an extremely focal distribution. Serous carcinoma reacted for CK (46 of 46 cases), EMA (46 of 46 cases), CA-125 (42 of 46 cases), S-100 protein (40 of 46 cases), Leu M1 (34 of 46 cases; with diffuse staining), B72.3 (33 of 46 cases), PLAP (29 of 46 cases), AM (15 of 46 cases), and CEA (six of 46 cases). Two profiles (S-100 + B72.3; S-100 + PLAP) were seen in 41 of 46 serous adenocarcinoma cases but were absent in all mesotheliomas. Hence, these combinations of determinants are effective in separating such neoplasms diagnostically. Moreover, diffuse reactivity for Leu M1, B72.3, PLAP, or CEA in papillary peritoneal neoplasms appears to exclude the possibility of mesothelioma; however, focal Leu M1 reactivity may indeed be seen in mesothelioma. Although CA-125 is a sensitive marker for serous carcinoma, it is not effective in distinguishing it from mesothelioma.

Immunophenotypic analysis of sinonasal non-Hodgkin's lymphomas

A panel of paraffin effective antibodies recognizing B cells and T cells (LN-2, MB1, L26, MT1, UCHL1, kappa, lambda) was used to characterize the immunophenotypes of 26 sinonasal non-Hodgkin's lymphomas. Seventeen tumors were stage I, five were stage II, one was stage III, and three were stage IV. Nine lymphomas were classified morphologically as large cell, six were large cell immunoblastic, six were small cleaved cell, two were mixed small and large cell, two were small noncleaved cell, and one was lymphoblastic. None were follicular. Twenty-two lymphomas had a B cell immunophenotype, three were T cell neoplasms, and one was immunoreactive only for MT1. This predominance of sinonasal lymphomas with a B cell immunophenotype in patients residing in the United States contrasts with the almost exclusive occurrence of T cell sinonasal lymphomas in Chinese patients living in Hong Kong and Japanese patients residing in regions of Japan that are nonendemic for human T cell leukemia virus-1.

Squamous cell carcinoma masquerading as focal myositis of the tongue

The diagnosis of squamous cell carcinoma of the head and neck is not usually a problem for the otolaryngologist/head and neck surgeon. However, we describe a patient whose ultimate diagnosis of squamous cell carcinoma required 16 months and eluded several clinicians, despite an aggressive diagnostic regimen. The diagnostic difficulty was due to the fact that the small, centrally located tumor was surrounded by an intense inflammatory reaction that histologically mimicked a recently described rare entity of the head and neck, focal myositis. Our purpose is to make the otolaryngologist/head and neck surgeon aware of this previously unreported presentation of squamous cell carcinoma of the tongue; to review the pertinent findings associated with focal myositis; and to reinforce the need to maintain a constant vigil for the diagnosis of cancer, in spite of negative pathologic confirmation, when dictated by the clinical situation.

Leiomyosarcoma of the urinary bladder. A clinicopathologic and immunohistochemical study of 15 cases

We present the clinicopathologic and immunohistochemical features of 15 vesical leiomyosarcomas. The nine male and six female patients ranged in age from 16 to 72 years (median: 49 years). Gross hematuria was the most common complaint. The tumors most often arose in the dome of the bladder (50%) and ranged in size from 1 to 10 cm (median: 5 cm). Five patients underwent total cystectomy, nine had a partial cystectomy or local excision, and one was only biopsied. Based on the highest of five sets of mitotic counts per case, eight tumors had one or fewer mitotic figures per 10 high-power fields (MF/10HPF); none of these patients developed metastases during a follow-up interval of 1 month to 20 years (mean: 62 months). Five tumors showed three to six MF/10HPF; one patient in this group died after 6 years with unresectable metastases, whereas the others are disease free with follow-up of 8 months to 8 years (mean: 62 months). Two tumors contained 10-15 MF/10HPF; one produced widespread metastases and was fatal after 3 months, whereas the other has not recurred or metastasized after 9 months. All tumors had infiltrating margins and invaded the bladder musculature--important features in their distinction from vesical leiomyoma. Nine leiomyosarcomas had zones of myxoid intercellular material; six of these were predominantly or exclusively myxoid. The myxoid foci often closely resembled inflammatory pseudotumor, particularly in superficial portions of the neoplasms. In two cases, an intense superficial plasma cell infiltrate mimicked a plasma cell granuloma. All 12 leiomyosarcomas studied immunohistochemically were negative for epithelial markers (cytokeratins and epithelial membrane antigen); staining for muscle-specific actin and vimentin was uniformly positive, and eight neoplasms also expressed desmin.

Gestational changes in calbindin-D9k in rat uterus, yolk sac, and placenta: implications for maternal-fetal calcium transport and uterine muscle function

Calbindin-D9k was quantified and its cellular location was defined in uterus, yolk sac, and placenta. In late gestation (days 17 to term) coordinated induction of calbindin-D9k was seen in uterine epithelial lining cells and juxtaposed yolk sac visceral epithelium as well as the intraplacental yolk sac epithelium. The induction of calbindin-D9k in these cells coincided with the time of exponential fetal bone growth and maximal fetal accumulation of calcium, suggesting a role of the protein in these epithelial layers in maternal-fetal calcium transport. Dynamic changes also occurred in the calbindin-D9k contents of the two layers of uterine smooth muscle (outer longitudinal and inner circular) during mid- and late gestation. During early pregnancy (days 0-4), calbindin-D9k was present in the two smooth muscle layers. By midgestation (day 10), calbindin-D9k had decreased by a factor of 10 in these tissue layers. During late gestation calbindin-D9k rebounded in the inner circular smooth muscle layer. These uterine changes of early and midgestation were reproduced by the endocrine changes of pseudopregnancy. Progesterone appeared to be a good candidate for controlling the midgestational decrease of uterine muscle calbindin-D9k, as it blunted estrogen's induction of the protein in the muscle layers and stroma in a dose-dependent manner. Changes in myometrial calbindin-D9k may reflect variations in muscular calcium storage, thereby representing alterations in potential for contraction.

Clenbuterol-induced desensitization in murine adipocytes: relationship to in vivo effectiveness

In vitro lipolytic response of isolated murine fat cells to epinephrine (EPI) or clenbuterol (CB) was used to evaluate the potential for the beta 2-adrenergic agonist, CB, to induce cellular resistance to further beta-adrenergic stimulation. Feeding CB (20 mg/kg diet) to mice for 1, 3 or 6 wk decreased adipocyte sensitivity to EPI or CB by 35-45%, with no differences in magnitude of this desensitization across time. Basal and maximal rates of lipolysis were similar for control- and clenbuterol-fed mice. In agreement with the feeding studies, a 2 hr preincubation of control-fat tissue with either 10 microM EPI or 100 microM CB, followed by adipocyte isolation and restimulation with EPI, reduced adipocyte sensitivity by 50%. In addition, maximal rates of lipolysis were decreased 24% and 34% for EPI and CB treated tissue, respectively. The similar adaptive responses of the adipocytes to CB exposure in vivo or in vitro suggest that CB interacts directly with fat cells in vivo and can induce tolerance. Mice fed CB for 12 wk had 33% smaller epididymal fat pads compared to controls, but pad weight differences were only 10% if feeding of CB was discontinued 1 wk before the 12 wk analysis. The reversal in fat pad gain with a 1 wk removal of CB from the diet indicates at least partial effectiveness of CB through 12 wk. The modest beta-adrenergic desensitization established by wk 1 was similar on wk 6 suggesting that CB-induced adipocyte resistance is of little consequence to the fat-reducing properties of CB administration.

Influence of the beta 2-adrenergic agonist clenbuterol on insulin-stimulated lipogenesis in mouse adipocytes

Growing mice fed the beta 2-adrenergic agonist clenbuterol (CB; 20ppm) had increased rate of growth and altered composition of gain (greater protein and less fat). Adipocytes prepared from the epididymal fat pads of treated and untreated mice were used to examine the influence of CB on lipid metabolism. Using cells from untreated mice, CB stimulated lipolysis to an equivalent maximum rate as epinephrine (EPI), but CB was far less potent (EC50 (microM); CB = 5, EPI = 0.2). Both CB and EPI inhibited insulin-stimulated lipogenesis over the physiological range of insulin concentrations. This inhibition was expressed as a dose-dependent decrease in tissue sensitivity to insulin and a decrease in maximal lipogenic capacity. Inhibition of maximal rate, but not of insulin sensitivity, could be stimulated by the addition of palmitate without EPI or CB. Adipocytes isolated from CB-treated mice did not differ from controls in sensitivity to insulin or in activity of fatty acid synthetase. Increased lipolysis and reduced lipogenesis as observed in vitro with CB are consistent with reduced fat accretion in CB-treated mice. However, the absence of detectable changes in adipocyte lipogenesis from CB-fed mice leaves open the question of the relevance of altered lipid metabolism to the observed changes in body composition.