Calcium mobilization and phosphatidylinositol turnover in vas deferens smooth muscle of diabetic rats

Ejaculatory dysfunction in men with diabetes mellitus

Diabetes mellitus (DM) is a metabolic disorder that is characterized by elevated blood glucose levels due to absolute or relative insulin deficiency, in the background of β-cell dysfunction, insulin resistance, or both. Such chronic hyperglycemia is linked to long-term damage to blood vessels, nerves, and various organs. Currently, the worldwide burden of DM and its complications is in increase. Male sexual dysfunction is one of the famous complications of DM, including abnormal orgasmic/ejaculatory functions, desire/libido, and erection. Ejaculatory dysfunction encompasses several disorders related to DM and its complications, such as premature ejaculation, anejaculation (AE), delayed ejaculation, retrograde ejaculation (RE), ejaculatory pain, anesthetic ejaculation, decreased ejaculate volume, and decreased force of ejaculation. The problems linked to ejaculatory dysfunction may extend beyond the poor quality of life in diabetics as both AE and RE are alleged to alter the fertility potential of these patients. However, although both diabetes patients and their physicians are increasingly aware of diabetic ejaculatory dysfunction, this awareness still lags behind that of other diabetes complications. Therefore, all these disorders should be looked for thoroughly during the clinical evaluation of diabetic men. Besides, introducing the suitable option and/or maneuvers to treat these disorders should be tailored according to each case. This review aimed to explore the most important findings regarding ejaculatory dysfunction in diabetes from pre-clinical and clinical perspectives.

Calcium homeostasis in vascular smooth muscle cells is altered in type 2 diabetes by Bcl-2 protein modulation of InsP3R calcium release channels

This study examines the extent to which the antiapoptotic Bcl-2 proteins Bcl-2 and Bcl-x(L) contribute to diabetic Ca(2+) dysregulation and vessel contractility in vascular smooth muscle cells (VSMCs) through their interaction with inositol 1,4,5-trisphosphate receptor (InsP(3)R) intracellular Ca(2+) release channels. Measurements of intracellular ([Ca(2+)](i)) and sarcoplasmic reticulum ([Ca(2+)](SR)) calcium concentrations were made in primary cells isolated from diabetic (db/db) and nondiabetic (db/m) mice. In addition, [Ca(2+)](i) and constriction were recorded simultaneously in isolated intact arteries. Protein expression levels of Bcl-x(L) but not Bcl-2 were elevated in VSMCs isolated from db/db compared with db/m age-matched controls. In single cells, InsP(3)-evoked [Ca(2+)](i) signaling was enhanced in VSMCs from db/db mice compared with db/m. This was attributed to alterations in the intrinsic properties of the InsP(3)R itself because there were no differences between db/db and db/m in the steady-state [Ca(2+)](SR) or InsP(3)R expression levels. Moreover, in permeabilized cells the rate of InsP(3)R-dependent SR Ca(2+) release was increased in db/db compared with db/m VSMCs. The enhanced InsP(3)-dependent SR Ca(2+) release was attenuated by the Bcl-2 protein inhibitor ABT-737 only in diabetic cells. Application of ABT-737 similarly attenuated enhanced agonist-induced [Ca(2+)](i) signaling only in intact aortic and mesenteric db/db vessels. In contrast, ABT-737 had no effect on agonist-evoked contractility in either db/db or db/m vessels. Taken together, the data suggest that in type 2 diabetes the mechanism for [Ca(2+)](i) dysregulation in VSMCs involves Bcl-2 protein-dependent increases in InsP(3)R excitability and that dysregulated [Ca(2+)](i) signaling does not appear to contribute to increased vessel reactivity.

Ejaculatory dysfunction in streptozotocin-induced diabetic rats: the role of testosterone

Hyperglycemic and hypoinsulinemic states caused by diabetes mellitus are usually related to some type of sexual dysfunction, resulting in infertility in humans and experimental models, mostly due to their effects on ejaculatory function. This study aimed to evaluate the possible role of testosterone in the restoration of normal ejaculatory function in diabetic rats. Male Wistar rats were randomly allocated into 3 experimental groups: control, diabetic (streptozotocin), and diabetic with testosterone supplementation (streptozotocin plus testosterone). The following parameters were assessed at the end of the experiment: body weight, circulating testosterone levels, number of spermatozoa ejaculated in the uterus through natural mating, and weight and in vitro isometric contractions of the vas deferens. Diabetic rats showed reduced plasma testosterone levels and ejaculatory dysfunction as observed by a lack in the spermatozoa ejaculated into the uterus of receptive females. In these diabetic rats, no difference was observed in the sensitivity of the vas deferens to norepinephrine, with or without the presence of the cocktail (cocaine plus propranolol). In spite of this, an increased sensitivity to methoxamine through the α1-adrenoceptor was observed. Testosterone supplementation did not restore these parameters to control values.We conclude that, in this experimental model, the lack of testosterone was not directly related to the diabetes-induced ejaculatory dysfunction.

Effects of streptozotocin-induced diabetes and insulin on calcium responsiveness of the rat vas deferens

In the present study, effects of streptozotocin-induced diabetes and insulin treatment on the reactivity of rat vas deferens to KCl and calmidazolium, a calmodulin antagonist, were evaluated and calmodulin levels in vas deferens tissue from diabetic and insulin-treated rats were determined. Diabetes was induced in rats by a single injection of streptozotocin. Five weeks after the induction of diabetes, one group of diabetic rats was injected with insulin for 3 weeks. After 8 weeks, vas deferens tissues on one side of diabetic and insulin-treated diabetic rats and their controls were mounted in organ bath to measure isometric tension, while the tissues on the other side of rats were homogenized to determine calmodulin levels by radioimmunoassay. Concentration-response curves to KCl were obtained in vas deferens tissues in the absence and presence of calmidazolium. The effects of KCl and calmidazolium on vas deferens isolated from 8-weeks diabetic rats were decreased. Calmodulin levels were also found to be decreased in vas deferens from diabetic rats. Decreased calmodulin levels in diabetic rat vas deferens were not corrected by insulin treatment. Only a partial correction following insulin treatment was observed in contractile effect of KCl on diabetic rat vas deferens, whereas insulin treatment increases the affinity of calmodulin in this muscle. Experimental diabetes causes an impairment in calcium/calmodulin-dependent contractile process of vas deferens, which is correctable partially following insulin therapy. The changes in the function of rat vas deferens due to streptozotocin diabetes seem to be related to impaired sexual functions in human diabetes.

Phosphodiesterase 5 Inhibitors in Rapid Ejaculation

Rapid (premature) ejaculation (RE) is a very common sexual disorder. This condition may be primary or secondary to underlying disease. Control of RE has been primarily focused on behavioural therapy, topical anaesthetics, tricyclic antidepressants and selective serotonin reuptake inhibitors; however, an approved treatment does not exist. Recently, a number of clinical trials have studied the potential effectiveness of the phosphodiesterase (PDE)-5 inhibitor sildenafil in the treatment of RE. Results of most of these studies have been encouraging. Available data indicate that there is clinical, anatomical, physiological, pharmacological and genetic evidence to explain the efficacy of PDE5 inhibitors in RE. The rationale for the use of PDE5 inhibitors in the treatment of RE could be due to possible peripheral and central mechanisms. Possible peripheral ejaculation retarding capabilities may include modulation of the contractile response of the vas deferens (VD), seminal vesicles (SV), prostate and urethra, induction of a state of peripheral analgesia, and prolongation of the total duration of erection. Possible central mechanisms may involve lessening of the central sympathetic output. Furthermore, there is evidence from knockout mice to explain the efficacy of PDE5 inhibitors in RE. Mice lacking the gene for endothelial nitric oxide synthase develop a condition similar to RE. On the other hand, mice lacking the gene for heme oxygenase-2 develop a condition similar to delayed ejaculation. This review also discusses the findings against the use of these agents in RE. In conclusion, a review of the literature suggests the potential usefulness of PDE5 inhibitors as a promising line of therapy in RE but further studies are needed.

Pharmacological comparison between the actions of methamphetamine and 1-aminoindan stereoisomers on sympathetic nervous function in rat vas deferens

The selective monoamine oxidase-B inhibitor selegiline (deprenyl) causes sympathomimetic effects and is metabolised to R(-)-methamphetamine and R(-)-amphetamine. The new monoamine oxidase-B inhibitor rasagiline is devoid of sympathomimetic effects and is metabolised to R(+)-1-aminoindan. Sympathomimetic effects of methamphetamine and 1-aminoindan enantiomers were compared in the rat vas deferens. R(-)-methamphetamine and S(+)-methamphetamine caused initial potentiation and subsequent inhibition of the field stimulation-induced twitch response of isolated rat vas deferens (0.1 Hz). EC(50) values for inhibition of twitch in prazosin-treated vas deferens were 0.36+/-0.13 and 1.64+/-0.10 microM (mean+/-S.E.M.) for S(+)- and R(-)-methamphetamine, respectively. There was no difference between S(+)-methamphetamine and R(-)-methamphetamine in potentiation of postsynaptic contractile response to noradrenaline. R(+)- and S(-)-1-aminoindan increased twitch response only at concentrations above 30 microM. R(-)-methamphetamine has similar potency to S(+)-methamphetamine in potentiation of noradrenaline-mediated responses and can therefore play a role in the sympathomimetic effects of selegiline.

Alternations of diacylglycerol kinase in streptozotocin-induced diabetic rats

Dysfunction of organs has been reported in diabetic rats, suggesting an association with changes in intracellular signal transduction pathways including phosphatidylinositol (PI) turnover. Diacylglycerol (DG) kinase catalyses the phosphorylation of DG, which is considered to play a major physiological role in the metabolism of the intracellular messenger DG. However, no relation between DG kinase activity and any disease in mammalian tissue has been reported to date. In the present study, we investigated whether the changes in DG kinase activity are related to diabetes. Basal resting level of DG kinase activity changed in tissue isolated from diabetic rats. Decreases in resting activity detected in aorta and kidney and agonist-induced responses differed between these tissues. Submaximal increases in basal activity also were detected in vas deferens and hepatocytes. These changes in DG kinase activity resemble the functional changes associated with complications of diabetes, suggesting that changes in PI turnover followed by DG kinase activity are a key element in the complications. It is the first study about the changes in DG kinase activity in mammalian disease.

Changes in electrophysiological properties and noradrenaline response in vas deferens of diabetic rats

The purpose of this study was to study changes in the sympathetic nerves of the vas deferens in 10-week-old streptozotocin-induced diabetic rats. To assess the activity of autonomic neurons, we recorded the amplitude and frequency of spontaneous junction potentials in vasa deferentia from age-matched controls and streptozotocin-induced diabetic rats. No change in the resting membrane potential of the smooth muscle of the vas deferens was found in streptozotocin-induced diabetic rats. The frequency of spontaneous junction potentials was significantly increased in the streptozotocin-induced diabetic rats and their amplitude was also markedly increased. The dose-response curve for the contractile response of the vas deferens to noradrenaline was significantly shifted to the right and the apparent affinity (pD2 value) was significantly decreased in streptozotocin-induced diabetic rats. These results suggest that degeneration of sympathetic neurons may occur in the vas deferens of 10-week streptozotocin-induced diabetic rats and that the greater amplitude of the spontaneous junction potentials may be related to an increase in Ca2+ mobilization, though the increase in Ca2+ mobilization does not lead to an enhanced contractile response.

In vivo signal-transduction pathways to stimulate phasic contractions in normal and inflamed ileum

We investigated the in vivo signal-transduction pathways to stimulate phasic contractions in normal and inflamed ileum by close intra-arterial infusions of test substances. Methacholine stimulated phasic contractions dose dependently. This response was suppressed during inflammation. Verapamil inhibited the response to methacholine dose dependently in both normal and inflamed ileum. Neomycin inhibited the response partially in normal ileum and almost completely in inflamed ileum. H-7 and chelerythrine partially inhibited the methacholine response in normal ileum but had no significant effect in inflamed ileum. Ryanodine stimulated phasic contractions that were blocked by TTX, hexamethonium, atropine, or ruthenium red. Ruthenium red, however, had no significant effect on the contractile response to methacholine.

CONCLUSIONS

1) Ca2+ influx through the L-type channels may be the primary source of Ca2+ to stimulate in vivo phasic contractions. 2) Phosphatidylinositol hydrolysis enhances the stimulation of in vivo phasic contractions in the normal ileum. In the inflamed ileum, phosphatidylinositol hydrolysis may be essential to stimulate phasic contractions. 3) Inflammation may downregulate the protein kinase C pathway. 4) Ryanodine stimulates phasic contractions by the release of ACh.

Norepinephrine-mediated calcium signaling is altered in vascular smooth muscle of diabetic rat

We studied the influence of diabetes on norepinephrine (NE)-induced changes in intracellular free Ca2+ levels (receptor-mediated Ca2+ signaling) in single tail artery vascular smooth muscle (VSM) cells. VSM cells from 12-16 week streptozotocin-induced diabetic (SID) rats showed an increase in sensitivity to NE when compared to control VSM cells in that the concentration of NE needed to elicit half maximal response of the initial Ca2+ transient was reduced more than 4-fold though the maximal response attained was apparently reduced. In addition, the slope factor (steepness) of the dose-response relation was lowered 4-fold. Moreover, VSM cells of diabetic animals had a higher incidence of NE-induced Ca2+ oscillatory responses. The shift of the dose-response curve to the left, coupled with a higher incidence of oscillations, indicate that the noradrenergic receptor-mediated Ca2+ signaling pathways in tail artery VSM of diabetic rat may be altered.

Effect of insulin treatment on smooth muscle calmodulin levels in rats with long-term streptozotocin-diabetes

Altered responses to several agonists have been reported in various smooth muscles from experimentally-diabetic animals suggesting a defective contractile process of smooth muscle. Recently, decreased smooth muscle calmodulin levels have been reported in streptozotocin-diabetic rats. However, the effectiveness of insulin on the decreased calmodulin levels in diabetic rats has not been questioned. Therefore, the present study was designed to examine the effect of insulin on smooth muscle calmodulin levels from streptozotocin-diabetic rats. Calmodulin levels of the smooth muscle were measured by a radioimmunoassay technique. Streptozotocin diabetes caused a significant decrease in tissue calmodulin levels of smooth muscles. Insulin therapy for 20 days did not correct the changes in calmodulin levels of rat smooth muscles, although it normalised blood glucose in streptozotocin-diabetic rats. These findings suggest that the altered smooth muscle calmodulin may contribute the defective contractile responses in diabetes and these changes may be resistant to insulin therapy.

Altered alpha-adrenergic responses of vas deferens to noradrenaline and tyramine from rats with short- and long-term alloxan diabetes

1. Functional and morphological abnormalities in vas deferens have been reported by both experimental and clinical studies as a cause of genital function abnormalities in diabetic males. 2. In the present study, contractile effects of noradrenaline and tyramine in isolated vas deferens from rats with short- and long-term alloxan diabetes were investigated by comparing with those from control rats. For this purpose, intrinsic activities (alpha E value) and apparent affinity constants (pD2 value) for contractile effects of noradrenaline and tyramine in the isolated rat vas deferens were calculated in normal rats and rats with short- and long-term alloxan diabetes. 3. Apparent affinity constants for contractile effects of noradrenaline in the isolated rat vas deferens were increased depending on both short- and long-term alloxan diabetes. By contrast, apparent affinity constants for contractile effects of tyramine in the isolated rat vas deferens were attenuated due to both short- and long-term alloxan diabetes. Intrinsic activities for both noradrenaline- and tyramine-induced contractions of rat vas deferens, however, were increased due to short-term diabetes and decreased due to long-term diabetes. 4. Experimental findings obtained in this study indicate that vas deferens preparations from rats with short- and long-term alloxan-induced diabetes exhibit altered alpha-adrenergic responsiveness depending on time elapsed. While short-term alloxan diabetes causes enhanced alpha-adrenergic responses in the rat vas deferens, the long-term diabetes decreases the responses in this tissue.

Effect of short and long term streptozotocin diabetes on smooth muscle calmodulin levels in the rat

Diabetes mellitus is a metabolic disease associated with certain complications which have also been demonstrated in the experimental models of this disease. Altered responses to several agonists have been reported in various smooth muscles from alloxan or streptozotocin diabetic animals. Since these reports revealed a defect in the contractile process of smooth muscles from experimentally-induced diabetes, short and long term effects of diabetes on calmodulin levels in the smooth muscles of aorta, trachea, vas deferens and duodenum were investigated using streptozotocin diabetic rats. In spite of the fact that most of the reports have demonstrated the defective contractions in long term diabetic rats, short term effect (for 1 week) of diabetes on calmodulin levels in the smooth muscles of aorta, trachea, vas deferens and duodenum was also investigated in the present study using streptozotocin diabetic rats to understand whether the changes in calmodulin dependent contractile process begin at an earlier stage of the disease. Tissue calmodulin levels of the smooth muscles were measured by the radioimmunoassay technique using a [125I]-labeled kit. Although rats injected with streptozotocin exerted the characteristics of diabetes such as polyuria, polydipsy, polyphagy and elevated blood glucose levels, unchanged calmodulin levels were found in the rats with short term streptozotocin diabetes. In contrast, long term streptozotocin diabetes (for 8 weeks) was found to cause a significant decrease in tissue calmodulin levels of these four smooth muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of trimebutine maleate on the contractile response of the isolated ileum from diabetic rats

1. Tension of the isolated ileum from diabetic rats induced by streptozotocin was measured isometrically to study the mode of action of trimebutine maleate (TMB). 2. The hyperreactivity of contractile response to KCl was observed in the isolated ileum from diabetic rats. TMB inhibited the contraction induced by KCl and acetylcholine (ACh) in normal solution. 3. In Ca2+ free solution, the hyperreactivity of contractile response to KCl was attenuated, and TMB did not inhibit the contraction induced by KCl. In contrast, TMB inhibited the contraction induced by ACh even in Ca2+ free solution. 4. These results suggest that the hyperreactivity of contractile response to KCl in the ileum from diabetic rats is due to the enhancement of Ca2+ influx through voltage-dependent Ca2+ channel and that TMB inhibits the hyperreactivity of contractile response through the inhibition of Ca2+ movement by the cell.

Comparative effects of loperamide hydrochloride on prostaglandin E1-induced contraction in isolated fundus and ileum of guinea pigs

The tension of isolated preparations of the fundus and the ileum of guinea pigs was measured isometrically to study the specific effect of loperamide hydrochloride on prostaglandin E1-induced contraction. Prostaglandin E1 caused concentration-dependent contraction in both the fundus and the ileum, and there was no significant difference between the fundus and the ileum. Loperamide hydrochloride inhibited prostaglandin E1-induced contraction in the fundus and the ileum. From the pD'2 value, loperamide hydrochloride caused greater inhibition of the contraction in the ileum than in the fundus. In a Ca(2+)-free solution containing 0.1 mM EGTA, prostaglandin E1-induced contraction in the ileum was almost eliminated, whereas 58% of the contraction in the fundus still remained. In Ca(2+)-free solution, loperamide hydrochloride and verapamil hydrochloride had no influence on prostaglandin E1-induced contraction, but markedly inhibited Ca(2+)-induced contraction. These results suggest that loperamide hydrochloride shows regional differences between gastrointestinal smooth muscles contracted by prostaglandin E1, and this may reflect one of the mechanisms in its antidiarrheal action through the suppression of peristalsis.

Calcium modulatory properties of 2,6-dibutylbenzylamine (B25) in rat isolated vas deferens, cardiac and smooth muscle preparations

1. In rat isolated vas deferens the new compound 2,6-dibutylbenzylamine (B25) evoked a series of repeating rhythmic contractions. Concentration-response curves constructed for this effect were bell-shaped, indicating a biphasic effect for this compound. By contrast, B25 depressed heart contractility without any visible positive inotropic or chronotropic activity. 2. Experiments with tetrodotoxin, reserpine, capsaicin, alpha-adrenoceptor blocking compounds and other agents permit us to exclude a release of neuromediators or a direct stimulation of post-synaptic receptors to account for the rhythmic effect of B25 in the rat vas deferens. 3. In the same tissue, the increase in 45Ca2+ uptake, the voltage-dependency as well as the dependence of the B25-induced rhythmic activity upon the external calcium concentration indicate a direct activation of voltage-sensitive calcium channels (VSCC). 4. Verapamil paradoxically stimulated the rhythmic effect of B25 in the rat vas deferens. La3+ was inactive while nifedipine was a weak inhibitor. By contrast Ni2+ and Mn2+ ions were good inhibitors (IC50 < 10(-4) M), suggesting that a possible opening of T-type VSCC underlies rhythmic effect of B25. 5. In radioligand binding studies competition experiments with [3H]-nitrendipine indicated that only at high concentrations was B25 able to interact with dihydropyridine-sensitive binding sites of heart and vas deferens smooth muscle. 6. B25 (3-30 microM) counteracted the inhibitory effects of omega-conotoxin GVIA in field-stimulated rat vas deferens.

The influence of streptozotocin-induced diabetes mellitus on the sensitivity of rat urinary bladder body and base strips to changes in extracellular calcium

1. The influence of calcium on contractile responses of bladders from control and 2 month streptozotocin-diabetic rats was investigated. 2. Removal of calcium from the bathing medium caused rapid decreases in the contractile responses of bladder body and base strips to carbachol. The responses of strips from control rats were reduced more by calcium removal than were strips from diabetics. 3. Replacement of calcium caused dose-dependent increases in contraction to carbachol. The responses of bladder body strips from diabetic rats to carbachol were significantly greater at all calcium concentrations than were those of controls. There were no differences in the responsiveness of bladder base strips to carbachol. 4. In contrast, bladder body strips from diabetic rats were more sensitive to calcium than were strips from controls, with an IC50 value for calcium of 0.38 mM vs 0.72 mM for controls. 5. At the calcium concentration of Krebs buffer (2.5 mM), contractile responses were near maximal, and there were no differences in sensitivity. 6. The calcium antagonist nifedipine caused dose-dependent decreases in the contractile responses of bladder base and body strips to nerve stimulation. The responses to nerve stimulation were more sensitive to nifedipine than were those to carbachol. There were no differences between controls and diabetics in the sensitivity of bladder strips to nifedipine. 7. The findings suggest that although increases in sensitivity to calcium are observed in bladder body strips from streptozotocin-diabetic rats, they are unlikely to be responsible for the increases in maximal contractile response to nerve stimulation and contractile agents.

Functional changes in vascular smooth muscle and endothelium of arteries during diabetes mellitus

To investigate the influence of diabetes mellitus on the responsiveness of the vascular smooth muscle, the effects of various vasoactive agents on the reactivity of the vascular smooth muscle from diabetic animals have been undertaken, focusing on the functional changes in the endothelium, alpha-adrenoceptors, beta-adrenoceptors, voltage-dependent Ca(2+)-channels, receptor-operated Ca(2+)-channels, phosphatidylinositol turnover and potassium channels. Among the functional changes, it is a common phenomenon that decreases in acetylcholine-induced production of cyclic GMP are due to the attenuation of release of endothelium-derived relaxing factor through an impairment of endothelium; this observation was found in both rats and rabbits with diabetes mellitus. These functional changes in diabetes may be responsible for the vascular complications such as coronary heart disease, cerebrovascular disease, and an acceleration in atherosclerosis.

Contractile responses and calcium mobilization in renal arteries of diabetic rats

The causes of diabetes-associated change of renal artery vasomotion have not been established. We investigated both contractile responses to KCl and norepinephrine (NE) in renal arteries of rats with streptozotocin-induced diabetes and age-matched controls and the effects on Ca2+ mobilization. Renal arteries from diabetics had greater maximum contractile responses to KCl and NE, but the threshold concentrations and EC50 values of KCl and NE were similar in controls and diabetics. The concentration-response for Bay K 8644, a dihydropyridine Ca2+ channel agonist in the presence of 20 mM KCl was significantly greater in diabetics than in controls. The maximum contractile responses to Ca2+ in the presence of 10(-6) M NE were significantly (P less than 0.05) greater in diabetics than in controls. The increased contractile response at low concentrations of Ca2+ (0.01-0.05 mM) was inhibited in both preparations by 10(-6) M nifedipine, but at high concentrations of Ca2+ (0.1-2.5 mM) the inhibition by nifedipine was significantly less in diabetics than in the controls. 45Ca2+ uptake had significantly greater resting levels in diabetics than in controls. The uptake of 45Ca2+ induced by 10(-5) M NE was significantly greater in diabetics than in controls, and 10(-7) M prazosin diminished both responses. The results suggest hyperreactivity of contractile responses to KCl or NE, and hyperpermeability of renal artery smooth muscle membrane to Ca2+ in streptozotocin-induced diabetics.

In vitro contractile responses of vasa deferentia from spontaneously diabetic BB rats

1. The effects of diabetes of 6 months' duration on autonomic function of the vas deferens were examined in spontaneously diabetic BB rats and diabetes-resistant BB rats. 2. Diabetes caused significant decreases in rat and testes weights, but had no effects on the weights of vasa deferentia compared to diabetes-resistant controls. 3. The contractile responses of vasa deferentia to nerve stimulation and to carbachol were increased compared to controls. However, the contractile responses of vasa deferentia from diabetic BB rats to ATP, phenylephrine, and 120 mM KCl were unaltered. 4. The increased responses to carbachol were associated with increases in the muscarinic receptor density, but no changes were detected in the number of dihydropyridine binding sites. 5. The data indicate that, in contrast to vasa deferentia from streptozotocin-diabetic rats which exhibit decreases in responsiveness to nerve stimulation and a non-specific supersensitivity to contractile agents, vasa deferentia from diabetic BB rats have no changes in sensitivity, and increased contractile responses to only nerve stimulation and carbachol. These differences in urogenital sensitivity to diabetes may be related to the insulin treatment which diabetic BB rats require to keep them alive.

Relations between contractile responses and beta-adrenoceptors in gastric fundus of diabetic rats

Contractile responses to norepinephrine (NE), and the population of beta-adrenoceptors, were determined in gastric fundus smooth muscle from rats with diabetes induced by streptozotocin (STZ), and age-matched controls. Relaxation and/or contraction of fundus strips of controls and diabetics were induced by 10(-5)M NE. Responses to NE were mainly relaxation in gastric fundus isolated from controls, and contraction in fundus isolated from diabetics. Contraction was blocked by 10(-8) M prazosin and relaxation was blocked by 10(-6) M propranolol. Relaxation by isoproterenol of contraction induced by 10(-6) M acetylcholine was significantly less in fundus from diabetics than in that from controls. The number of beta-adrenoceptors, measured with [125I] iodocyanopindolol as a ligand, was significantly less in gastric fundus membrane isolated from diabetics than in that from controls, but affinity was no different. The level of plasma catecholamine was higher in diabetics than in controls. Results suggest that depression of gastric fundus relaxation and increase of contraction by NE in diabetics could be due to fewer beta-adrenoceptor binding sites caused by down-regulation by higher catecholamine level in diabetic rats.