Chronic cyclosporin nephropathy: long-term effects of cyclosporin on renal allografts

Cyclosporin (CSA) has significantly reduced both incidence and severity of acute rejection, and brought excellent graft survival rates. Chronic CSA nephrotoxicity seems to be the second most important diagnosis responsible for the late graft failure. CSA-associated arteriolopathy (CAA) is well known as a characteristic lesion of chronic CSA nephrotoxicity by graft biopsies. There are few reports on the long-term outcome of renal transplant patients with biopsy-proven chronic CSA nephrotoxicity after diagnosis of CAA. We conducted two studies, the long-term outcome of the patients with CAA, and the FGS lesion related to CAA. Seventy-four CAA patients continued on CSA therapy after diagnosis of CAA were classified into two groups by outcome of the graft after follow-up: the functioning graft group (n = 30) and the graft-loss group (n = 44). There was no significant difference in severity of CAA grade between the functioning and graft-loss groups. Concomitant lesion of chronic rejection but not severity of CAA was the most important risk factor of graft loss for CAA patients in our study. Of a total of 54 recipients with FGS lesion, 32 patients (59%) were diagnosed as CAA-associated glomerulopathy (CAG) accompanied with severe CAA. Eighteen of 32 CAG patients lost their grafts after follow-up. Their serum creatinine level at biopsy was higher than that of the functioning group; however, there was no significant difference in daily proteinuria at biopsy between two groups. We have tried to reduce CSA dosage to maintain lower blood levels than the usual optimal target levels, but did not discontinue CSA after diagnosis of severe CAA and FGS lesion. In 15 isolated pure CAG patients, those with increasing daily proteinuria exceeding 2 g lost their graft function even after reducing CSA administration. The change in daily proteinuria seems to be a useful indicator for late graft loss in the patients of FGS lesion with severe CAA. CAA is not specific for chronic CSA nephrotoxicity, and FGS lesion is also a non-specific lesion often developed in renal allografts. Our study revealed clinicopathological characteristics of chronic CSA nephrotoxicity. Isolated chronic CSA arteriolopathy of severe degree has a fairly good prognosis under controlled CSA therapy. FGS lesion accompanied by CAA is considered as a new concept of CAG, and increasing proteinuria in patients with CAG is a good indicator for poor outcome. These results will contribute towards an appropriate therapeutic plan for renal transplant patients undergoing long-term CSA treatment.

Does infiltration of neutrophils in peritubular capillaries indicate humoral rejection? A case displaying a characteristic lesion of a significantly high amount of neutrophils in peritubular capillaries at 1-h graft biopsy during transplant operation

We present a case report of a 50-yr-old Japanese woman with a significant accumulation of neutrophils in the peritubular capillaries (PTC) and severe acute tubular necrosis (ATN) at 1-h allograft biopsy during transplant operation from cadaver donor after a cardiac death. Significant accumulation of neutrophils in the PTC is usually valuable diagnostically for acute humoral rejection. However, the patient showed no clinical signs of acute rejection. A second graft biopsy performed on the fifth postoperative day (POD) revealed that both infiltration of neutrophils in PTC and ATN lesions were more aggravated. Neither clinical course nor other morphological findings were compatible with humoral rejection. After the third biopsy of POD 27 revealing acute vascular rejection of moderate degree, acute rejection therapy using methylprednisolone pulse therapy and OKT-3 therapy was performed. Consequently, after a period of delayed graft function requiring haemodialysis for approximately 4 wk, graft function was restored and serum creatinine decreased to 2 mg/dL. Later, we were able obtain information from a paired graft from the same donor. Significant accumulation of neutrophils in the PTC similar to our recipient was also noted in a 1-h biopsy specimen of the paired kidney. This confirmed that the accumulation of neutrophils in the PTC noted in two recipients was transmitted from the donor kidney. The pathogenesis and clinical significance of neutrophils in the PTC has been shrouded in mystery.

Correlation of Lorenz scatterplots with frequency-domain heart rate variability

Heart rate (HR) variability is important with respect to disease prognosis and the effects of drugs. Lorenz scatterplots provide a simple way to evaluate HR variability visually. The relation of Lorenz scatterplots to frequency-domain HR variability was examined in 75 Holter recordings and in simulated HR trends. The length of Lorenz scatterplots was double-exponentially correlated with total frequency and very-low frequency powers, with correlation coefficients (r) of 0.88. The width of Lorenz scatterplots was highly correlated with the high frequency power (r=0.98). The sum of the width and length of Lorenz scatterplots was highly correlated with the total frequency power (r=0.92). Identical results were obtained when simulated HR trends were used. In conclusion, Lorenz scatterplots provide a simple way to estimate the frequency-domain HR variability.

Simultaneous multi-site recordings of neural activity with an inline multi-electrode array and optical measurement in rat hippocampal slices

Understanding neuronal network function requires multi-site recording. An optical imaging method using voltage-sensitive dyes (VSD) is one such suitable method. It is also important to complement this technique with methods that measure other physiological parameters of neuronal network activity. We aimed to develop a multi-channel electrode method that would easily permit the simultaneous optical imaging of neural activity in vitro. There are several multi-electrode systems; some of these are commercially available, but they are not easy to use and are also expensive. We developed a novel, less expensive, stainless steel inline electrode array that utilizes the standard etching method of circuit board manufacturing. This method, along with widely available computer drawing software, allowed us to produce electrode arrays with uniform quality in electrical characteristics and shapes. The electrode array was designed so that it could easily substitute for single electrode systems without modifying the conventional set-up used for electrophysiological measurements and optical recordings. Simultaneous measurement of evoked neural activities in area CA1 of the rat hippocampal slice with our optical imaging method using the VSD Di-4-ANEPPS is demonstrated in this paper. The electrode array was also used as a stimulating electrode, and the evoked response was measured by the optical recording method. The results demonstrate the advantages of simultaneous recordings obtained by these complementary multi-site recording methods in vitro.

Upregulation of matrix metalloproteinase-1 production by prostaglandin F2alpha in human gingival fibroblasts

In the present study, we investigated the effect of prostglandin F2alpha (PGF2alpha) and combination of PGF2alpha and interleukin(IL)-1beta on matrix metalloproteinase (MMP)-1 production in human gingival fibroblasts (HGF). PGF2alpha enhanced MMP-1 production in a dose-dependent manner in HGF. Combination of PGF2alpha and IL-1beta induced a synergistic increase of MMP-1 production in HGF. Furthermore, fluprostenol, a specific FP receptor agonist, increased MMP-1 production and induced a synergistic enhancement of IL-1beta-induced MMP-1 production in HGF, similar to PGF2alpha. FP receptor mRNA expression was detected in HGF, by reverse transcription-polymerase chain reaction. Northern blot analysis revealed that PGF2alpha enhanced MMP-1 mRNA expression in HGF and that PGF2alpha increased MMP-1 mRNA levels induced by IL-1beta. In conclusion, we suggest that PGF2alpha increases MMP-1 production in HGF and synergistically enhances MMP-1 production in IL-1beta-stimulated HGF. PGF2alpha may be involved in degradation of connective tissue in periodontal lesions.

Osteoprotegerin levels before and after renal transplantation

Osteoprotegerin (OPG) is a newly identified glycoprotein that belongs to the tumor necrosis factor receptor superfamily and regulates bone mass by inhibiting osteoclastic bone resorption. The regulatory mechanism of OPG is still unclear after successful renal transplantation (RTX), however, resulting in resolution of uremia. The present study was designed to clarify the potential role of OPG in uremia and after RTX under immunosuppressive therapy. We evaluated circulating OPG levels by measuring them before and after RTX (postoperative days 2, 14, and 28). Our protocol of immunosuppressive drugs was dual therapy using cyclosporine and steroids. Serum OPG was quantitated using enzyme-linked immunosorbent assay. After successful RTX, serum OPG levels decreased significantly on day 14 and day 28 compared with the baseline level (P < 0.05). Creatinine clearance dramatically increased until day 14 and decreased thereafter. Serum OPG declines for the first 2 weeks after RTX owing to functioning allograft and decreases again for the next 2 weeks because of steroids and possible immunosuppressive agents.

More than 1,000 cases of total parathyroidectomy with forearm autograft for renal hyperparathyroidism

Between March 1981 and December 2000, we performed 1,053 total parathyroidectomies with forearm autograft for advanced renal hyperparathyroidism (HPT). Based on histopathologic and pathophysiologic investigations, surgical treatment should be considered when parathyroid glands show nodular hyperplasia. Measuring parathyroid volume by ultrasonography was useful to detect nodular glands and to determine surgical indications. The clinical effect of parathyroidectomy on the symptoms and biochemical variables was striking. Skeletal deformity, progressive bone loss, and vessel calcification leading to high mortality risk could not be alleviated by even successful surgery, however. To prevent cardiovascular complications, parathyroidectomy should be performed in the relatively early stage of renal HPT. Total parathyroidectomy with forearm autograft is a suitable procedure for renal HPT, especially in patients who require long-term hemodialysis. For surgeons, it is important to remove all parathyroid glands, including supernumerary glands, at the initial operation and to choose adequate parathyroid tissue for the autograft to prevent persistent and recurrent HPT. Although the risk of graft-dependent recurrent HPT is not negligible, enlarged transplanted parathyroid tissue can be removed easily and noninvasively from the forearm under local anesthesia. There is no risk of hypofunction of the autograft.

Spontaneous tumorigenesis in mice defective in the MTH1 gene encoding 8-oxo-dGTPase

Oxygen radicals, which can be produced through normal cellular metabolism, are thought to play an important role in mutagenesis and tumorigenesis. Among various classes of oxidative DNA damage, 8-oxo-7,8-dihydroguanine (8-oxoG) is most important because of its abundance and mutagenicity. The MTH1 gene encodes an enzyme that hydrolyzes 8-oxo-dGTP to monophosphate in the nucleotide pool, thereby preventing occurrence of transversion mutations. By means of gene targeting, we have established MTH1 gene-knockout cell lines and mice. When examined 18 months after birth, a greater number of tumors were formed in the lungs, livers, and stomachs of MTH1-deficient mice, as compared with wild-type mice. The MTH1-deficient mouse will provide a useful model for investigating the role of the MTH1 protein in normal conditions and under oxidative stress.

Early changes of bone histology and circulating markers of bone turnover after parathyroidectomy in hemodialysis patients with severe hyperparathyroidism

AIMS

There have so far been no reports on the changes in bone histology in the early period after parathyroidectomy and autografting (PTX-AG). We investigated the effects of PTX-AG on bone histology during the initial 12 weeks after undergoing these surgical procedures.

MATERIALS AND METHODS

We performed bone histomorphometry 3 times (before as well as 4 and 12 weeks after PTX-AG) in 6 patients and 2 times (before and 4 weeks after PTX-AG) in 3 hemodialysis patients. In addition, the circulating parameters of bone metabolism were also assessed before and after PTX-AG in all 9 patients. The changes in the histomorphometric (static) parameters between pre-surgery and 4 weeks after surgery and those between 4 weeks and 12 weeks after surgery were assessed by the t-test while changes in the circulating parameters of bone metabolism were analyzed by Friedman's test.

RESULTS

Bone formation parameters including carboxy terminal propeptide of human type I procollagen (PICP), alkaline phosphatase (ALP) and intact osteocalcin (i-OC) were all extremely high before surgery. These parameters initially increased after PTX-AG and thereafter gradually declined. In contrast, the circulating bone resorption parameters including tartrate-resistant acid phosphatase (TRAP) and deoxypyridinoline (Dpyr) were also extremely high at baseline but markedly declined after operation. Osteoid-related parameters including osteoid volume (OV/BV), osteoid surface (OS/BS), and osteoid thickness (O.Th) all initially increased at 4 weeks after PTX-AG. In contrast, osteoblast surface (Ob.S/BS), osteoclast surface (Oc.S/BS), eroded surface (ES/BS), and fibrosis volume (Fb.V/TV) all decreased at 4 weeks after surgery, while Ob.S/BS decreased further at 12 weeks in cases 1-6. Although bone mineralization was ongoing at 4 weeks after surgery, both the mineral apposition rate (MAR) and bone formation rate (BFR) remained below the mean for normal individuals.

CONCLUSIONS

The circulating bone formation parameters and osteoid-related parameters showed an initial increase after PTX-AG. The concomitant decline in the circulating bone resorption parameters reflected the reduction in bone resorption. BFR decreased, but bone mineralization did not stop after PTX-AG.

A novel alpha-amino-acid esterase from Bacillus mycoides capable of forming peptides of DD- and DL-configurations

A novel alpha-amino-acid esterase possessing some properties favorable for the synthesis of D-amino acid-containing peptides has been purified from the culture broth of Bacillus mycoides. The enzyme consisted of 4 subunits of 39 kDa, had an isoelectric point of 7.0, and showed its maximum activity at around 47 degrees C and pH 7.6. The enzyme activity was strongly depressed by phenylmethanesulfonyl fluoride, but not by penicillin G or ampicillin, suggesting that the protein is a serine enzyme lacking penicillin-binding ability. The enzyme hydrolyzed a variety of D- and L-amino acid methyl esters with concomitant formation of homooligomers from D-Phe, D-Trp, D-Tyr, and D-Asp(OCH(3)) methyl esters, but it did not act on the D- or L-amino acid amides tested. Incubation of a mixture of Ac-D-Phe-OMe and D-/L-Leu-NH(2) with the enzyme yielded Ac-D-Phe-D-/L-Leu-NH(2) together with Ac-D-Phe-OH, the hydrolysate of the carboxyl component. To its credit, the enzyme failed to hydrolyze casein as well as peptides including diastereomers of diphenylalanine and dialanine, indicating that the enzyme would not cause secondary hydrolysis of once-formed peptides. These observations indicate the potential utility of the newly isolated enzyme for the synthesis of D-amino acid-containing peptides.

Acute humoral rejection of kidney allografts in patients with a positive flow cytometry crossmatch (FCXM)

The patients with a positive flow cytometry crossmatch (FCXM) are categorized as a high-risk group causing hyperacute or accelerated acute rejection after kidney transplantation. According to the successful results of ABO-incompatible renal transplantation, we have performed the living related transplant operations in the recipients with positive FCXM for donor T cells, but having a negative complement-dependent lymphocytotoxic reaction test. We have followed the clinical course of 4 FCXM-positive patients, and 2 of them have developed acute humoral rejection. We report the strategies for FCXM-positive living kidney transplantations and the characteristics of pathological findings of acute humoral rejection in FCXM-positive renal transplants. We have had few episodes of acute humoral rejection in ABO-incompatible kidney transplantations under immunosuppressive regimens, including cyclophosphamide, but 2 patients of 4 with FCXM-positive kidney transplantations developed acute humoral rejections. The differences in immunosuppressive regimen between ABO-incompatible and FCXM-positive kidney transplantations concern anti-lymphocyte globulin (ALG) and splenectomy. We have not performed splenectomy and ALG administration in FCXM-positive kidney transplantations. Severe acute rejection episodes have been experienced on post-operative days 7 and 9 in 2 of 4 FCXM-positive recipients. The early acute rejection episodes were clinically and pathologically diagnosed as typical humoral rejections. We have examined an immunofluorescent study to prove the diagnosis of humoral rejection in FCXM-positive kidney transplantations; both immunoglobulin M and C3 were positive for the whole course of humoral rejection. The 2 patients with acute humoral rejection recovered after treatment with double filtration plasmapheresis or plasma exchange to remove their anti-donor antibodies. The gold standard of success in FCXM-positive kidney transplantations is to suppress the production and reduce the level of anti-donor antibodies after transplant operations.

Statistical analysis of diagnostic failure of fine needle aspiration cytology (FNAC) in breast cancer

Fine-needle aspiration cytology (FNAC) was performed on 300 patients. Among those, 57 cases failed in accurate diagnosis of malignancy and 243 were successful. Fourteen clinicopathological factors altogether were analyzed to elucidate any correlation with FNAC failure using uni- and multivariate analysis. The univariate analysis in each clinicopathlogical factor showed that these error cases were vaguely palpable cancers, estrogen receptor (ER) positive cancers, small-sized of tumors, scattered type of cancer cell distribution in tumor tissues, with low tumor grade, with low Nottingham prognostic index (NPI), with benign-like ultrasound findings and with low TNM stage. The multivariate analysis revealed tumor grade was the strongest factor for all, followed by cellular distribution type of cancer cells and benign-like ultrasound findings. From these results, we speculated that diagnostic failure of FNAC at first clinic visit seemed to be caused by mainly two histocytological factors: extrinsic factor (structural factors of tissue-like tumor cells' distribution pattern, etc.); and intrinsic one (cellular factors of low atypism such as benign-like ultrasound finding, low tumor grade, and so on).

Inhibitory effects of amlexanox on carbachol-induced contractions of rabbit ciliary muscle and guinea-pig taenia caecum

Instillation of amlexanox, an anti-allergic drug, over a long period improves myopia in some allergy patients and in monkeys. The relaxing effect of amlexanox on persistent contraction of ciliary muscle may be involved in the improvement of myopia. In this study, the mechanism of the noncompetitive inhibition of carbachol-induced contractions by amlexanox (1-100 microM) was investigated in isolated smooth muscle preparations of the rabbit ciliary body and guinea-pig taenia caecum. In ciliary muscles, amlexanox (100 microM) inhibited both the phasic and tonic components of carbachol-induced contractions even in the presence of cyclopiazonic acid (10 microM) where the function of the sarcoplasmic reticulum was impaired, while diltiazem (3.2, 32 microM) did not. In taenia caecum, diltiazem (3.2 microM) slightly inhibited the phasic component and abolished the tonic component of carbachol-induced contractions. Amlexanox also abolished the tonic component, but it did not decrease the 45Ca2+ uptake into taenia caecum smooth muscle cells induced by carbachol. Amlexanox did not increase the cyclic adenosine monophosphate (cyclicAMP) content of ciliary muscles in the presence of 3-isobutyl-1-methylxanthine (10 microM), while forskolin (1 microM) did. Gel-shift assay showed that the inhibition of carbachol-induced contractions by amlexanox was accompanied by a decrease in phosphorylation of the 20-kDa myosin light chain in taenia caecum tissue preparations. Amlexanox had no effect on calmodulin activity, whereas it inhibited phosphorylation of the myosin light chain by purified myosin light-chain kinase from chicken gizzard. These results suggested that amlexanox may not affect either Ca2+ mobilization or calmodulin activity, although it inhibits myosin light-chain kinase, which may inhibit carbachol-induced contraction.

Quantification of optical signals with electrophysiological signals in neural activities of Di-4-ANEPPS stained rat hippocampal slices

We have quantified the optical signals of synaptically induced neural activities in an in vitro brain slice preparation in terms of electrophysiological signals. The qualification was done using electrophysiologically well known neural activities in the CA1 area of rat hippocampal slices stained with externally applied fluorescent voltage-sensitive dye (VSD; Di-4-ANEPPS). Together with a newly designed CCD-based digital high-speed camera system and epi-fluorescent optics, our improvements were made on a protocol for staining using a newly designed chamber system. These improvements enabled us to make stable and reliable recordings of optical signals and electrophysiological measurements without affecting the physiological status and to make a quantitative comparison between them. The time course and amplitude of the optical signal showed fair agreement with intracellular and extracellular recordings, and was stable over 2 h. The optical signal followed synaptically induced long-term potentiation (LTP) as monitored by the electrophysiological signals. A regional difference in the amount of LTP was found in optical signals and was confirmed in the electrophysiological signals. These results demonstrate the capabilities of our improved method as an alternative but more potent tool to measure the neuronal activities of brain slice in addition to electrophysiological method.

High serum concentrations of soluble E-selectin in patients with impaired glucose tolerance with hyperinsulinemia

High serum concentrations of soluble adhesion molecules are present in diabetics, but whether similar levels are present in patients with impaired glucose tolerance (IGT) is unclear. We measured serum concentrations of soluble intercellular adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVCAM-1), and sE-selectin in 128 nondiabetic Japanese subjects. The concentrations of sICAM-1, sVCAM-1, and sE-selectin in IGT patients (n=47) were not different from those in subjects with normal glucose tolerance (NGT; n=81). IGT patients were subdivided into two groups by the results of 75 g OGTT, those with low- (hypoinsulinemia; n=23) or high-insulin (hyperinsulinemia; n=24). The levels of sICAM-1 and sVCAM-1 were not different among NGT and IGT with high-insulin or with low-insulin. However, sE-selectin concentrations were significantly higher in IGT patients with high-insulin than in NGT and IGT with low-insulin (61.1+/-3.4, 47.1+/-1.8 and 43.7+/-3.9 ng/ml, respectively, P<0.001). Adjustment for age and gender did not influence the results. Serum sE-selectin concentrations correlated significantly with the area under the curve of insulin (AUC(insulin)), AUC(glucose), diastolic blood pressure, and triglyceride levels (r=0.35, 0.26, 0.18 and 0.21, respectively), and negatively with HDL-cholesterol levels (r=-0.20). Multiple regression analysis showed that AUC(insulin) was the only independent factor that correlated with sE-selectin levels (P<0.001). Our results indicate that hyperinsulinemia/insulin resistance may be responsible for the elevation of sE-selectin levels.

Secretory leukoprotease inhibitor augments hepatocyte growth factor production in human lung fibroblasts

Secretory leukoprotease inhibitor (SLPI), an 11.7-kD nonglycosylated serine protease inhibitor, is produced and released into the fluids of mucosal surfaces including human lung. It comprises two domains with homologous amino acid sequences: the N-terminal domain possessing antibacterial activity, and the C-terminal domain with antiprotease activity. Here we report the positive regulation of hepatocyte growth factor (HGF) production in human lung fibroblasts exerted by SLPI or its C-terminal domain under physiologic concentrations (1 to 10 microM). This HGF production by SLPI was unaffected by the addition of interleukin (IL)-1 receptor antagonist. In contrast, human skin fibroblasts exerted no SLPI-stimulated increase in HGF production, despite the fact that IL-1beta increased HGF production with an intensity similar to that of human lung fibroblasts. Both the time-course and dose-response studies in human lung fibroblasts revealed that the induction of HGF messenger RNA (mRNA) and protein occurred in parallel, indicating that the mechanism existed at the steady-state mRNA level. A synthetic elastase inhibitor failed to induce HGF, but alpha(1)-antitrypsin also stimulated HGF production in lung fibroblasts. Inactivation of the antiprotease activity of SLPI or its C-terminal domain by an oxidizing agent (N-chlorosuccinimide) abolished their stimulatory effect on HGF production. These findings demonstrate that SLPI exerts a novel HGF induction and functions as an anti-inflammatory and regenerative factor in addition to its role in protease inhibition.

Increased insulin sensitivity and decreased insulin secretion in offspring of insulin-sensitive type 2 diabetic patients

To investigate the early defects of glucose metabolism in insulin-sensitive type 2 diabetes, we performed oral and frequently sampled intravenous glucose tolerance tests (OGTT and FSIGT) with minimal model analysis in 15 offspring of Japanese type 2 diabetics with normal insulin sensitivity (insulin resistance index of homeostasis model assessment [HOMA-R] < 2.0) and in 20 healthy control subjects without a family history of type 2 diabetes. The frequency of impaired glucose tolerance (IGT) was 40% (6 of 15) in the offspring and 0% (0 of 20) in the controls. Fasting plasma glucose (4.8 +/- 0.1 v4.6 +/- 0.1 mmol/L, P = .18) and immunoreactive insulin ([IRI] 29.9 +/- 2.5 v 28.3 +/- 2.5 pmol/L, P = .64) were comparable between the offspring and the controls. The rate of glucose disappearance (KG) was significantly lower in the offspring versus the control group (2.00 +/- 0.22 v 2.60 +/- 0.17 min(-1), P= .03). The insulin sensitivity index (Si) was significantly greater in the offspring versus the controls (2.68 +/- 0.41 v 1.71 +/- 0.17 x 10(-4) min(-1) x pmol/L , P = .02). First-phase insulin secretion (FPI) to intravenous glucose was significantly lower in the offspring versus the control group (886 +/- 110 v 2,296 +/- 267 min x pmol/L, P< .01). Glucose effectiveness (SG) was comparable between the offspring and control groups. The disposition index (Si x FPI) was significantly lower in the offspring versus the controls (2,106 +/- 256 v 3,652 +/- 490 x 10(-4), P = .02). When the offspring were subdivided into 2 groups by glucose tolerance status, both normal glucose tolerance (NGT) offspring and IGT offspring showed a significant decrease in FPI and increase in Si. Thus, although the offspring of insulin-sensitive type 2 diabetics had increased insulin sensitivity, the impairment in insulin secretion was more dominant. Our results suggest that the early metabolic abnormality in insulin-sensitive type 2 diabetes is an insulin secretory dysfunction despite increased insulin sensitivity.

Exponential hyperbolic sine function fitting of heart rate response to constant load exercise

We attempted to fit heart rate (HR) changes induced by constant exercise loads of different intensities to an exponential hyperbolic sine curve by the least-squares method, and we compared the results with the fitting of the changes to exponential curves. Seven healthy male volunteers performed three different intensities of constant-load exercise on a bicycle ergometer. The exponential hyperbolic sine function adequately fitted the HR responses induced by all three different intensities of loads: low (30 W: correlation coefficient, r = 0.68 +/- 0.13, mean +/- SD), moderate (75 W: r = 0.93 +/- 0.07) and high (125 W: r = 0.97 +/- 0.02). The first-order exponential curve fitted only the moderate load response. Although the second-order exponential equation fitted the HR response for both the moderate and high loads, the equation did not fit the low-load response (r = 0.43 +/- 0.26). In low-load exercise, the sum of the power of the residuals for the exponential hyperbolic sine curve fitting was significantly smaller than that for the first- or second-order exponential curve fitting. In conclusion, the exponential hyperbolic sine function is useful for quantitative analyses of the HR response to exercise loads of various intensities.