The reversal effect of insulin on diabetes-induced alterations in beta adrenergic and muscarinic receptors in rat prostate

Established and emerging treatments for diabetes-associated lower urinary tract dysfunction

Dysfunction of the lower urinary tract (LUT) including urinary bladder and urethra (and prostate in men) is one of the most frequent complications of diabetes and can manifest as overactive bladder, underactive bladder, urinary incontinence, and as aggravated symptoms of benign prostate hyperplasia. We have performed a selective literature search to review existing evidence on efficacy of classic medications for the treatment of LUT dysfunction in diabetic patients and animals, i.e., α1-adrenoceptor and muscarinic receptor antagonists, β3-adrenoceptor agonists, and phosphodiesterase type 5 inhibitors. Generally, these agents appear to have comparable efficacy in patients and/or animals with and without diabetes. We also review effects of antidiabetic medications on LUT function. Such studies have largely been performed in animal models. In the streptozotocin-induced models of type 1 diabetes, insulin can prevent and reverse alterations of morphology, function, and gene expression patterns in bladder and prostate. Typical medications for the treatment of type 2 diabetes have been studied less often, and the reported findings are not yet sufficient to derive robust conclusions. Thereafter, we review animal studies with emerging medications perhaps targeting diabetes-associated LUT dysfunction. Data with myoinositol, daidzein, and with compounds that target oxidative stress, inflammation, Rac1, nerve growth factor, angiotensin II receptor, serotonin receptor, adenosine receptor, and soluble guanylyl cyclase are not conclusive yet, but some hold promise as potential treatments. Finally, we review nonpharmacological interventions in diabetic bladder dysfunction. These approaches are relatively new and give promising results in preclinical studies. In conclusion, the insulin data in rodent models of type 1 diabetes suggest that diabetes-associated LUT function can be mostly or partially reversed. However, we propose that considerable additional experimental and clinical studies are needed to target diabetes itself or pathophysiological changes induced by chronic hyperglycemia for the treatment of diabetic uropathy.

Can Antidiabetic Drugs Improve Male Reproductive (Dys)Function Associated with Diabetes?

The alarming increase in the number of diabetic patients worldwide raises concerns regarding the impact of the disease on global health, not to mention on social and economic aspects. Furthermore, the association of this complex metabolic disorder with male reproductive impairment is worrying, mainly due to the increasing chances that young individuals, at the apex of their reproductive window, could be affected by the disease, further contributing to the disturbing decline in male fertility worldwide. The cornerstone of diabetes management is glycemic control, proven to be effective in avoiding, minimizing or preventing the appearance or development of disease-related complications. Nonetheless, the possible impact of these therapeutic interventions on male reproductive function is essentially unexplored. To address this issue, we have made a critical assessment of the literature on the effects of several antidiabetic drugs on male reproductive function. While the crucial role of insulin is clear, as shown by the recovery of reproductive impairments in insulin-deficient individuals after treatment, the same clearly does not apply to other antidiabetic strategies. In fact, there is an abundance of controversial reports, possibly related to the various study designs, experimental models and compounds used, which include biguanides, sulfonylureas, meglitinides, thiazolidinediones/glitazones, bile acid sequestrants, amylin mimetics, as well as sodiumglucose co-transporter 2 (SGLT2) inhibitors, glucagon-like peptide 1 (GLP1), α-glucosidase inhibitors and dipeptidyl peptidase 4 (DPP4) inhibitors. These aspects constitute the focus of the current review.

Antidiabetic therapies and male reproductive function: where do we stand?

Diabetes mellitus has been increasing at alarming rates in recent years, thus jeopardizing human health worldwide. Several antidiabetic drugs have been introduced in the market to manage glycemic levels, and proven effective in avoiding, minimizing or preventing the appearance or development of diabetes mellitus-related complications. However, and despite the established association between such pathology and male reproductive dysfunction, the influence of these therapeutic interventions on such topics have been scarcely explored. Importantly, this pathology may contribute toward the global decline in male fertility, giving the increasing preponderance of diabetes mellitus in young men at their reproductive age. Therefore, it is mandatory that the reproductive health of diabetic individuals is maintained during the antidiabetic treatment. With this in mind, we have gathered the available information and made a critical analysis regarding the effects of several antidiabetic drugs on male reproductive function. Unlike insulin, which has a clear and fundamental role on male reproductive function, the other antidiabetic therapies' effects at this level seem incoherent. In fact, studies are highly controversial possibly due to the different experimental study approaches, which, in our opinion, suggests caution when it comes to prescribing such drugs to young diabetic patients. Overall, much is still to be determined and further studies are needed to clarify the safety of these antidiabetic strategies on male reproductive system. Aspects such as the effects of insulin levels variations, consequent of insulin therapy, as well as what will be the impact of the side effect hypoglycemia, common to several therapeutic strategies discussed, on the male reproductive system are still to be addressed.

Obesity and metabolic dysfunction severely influence prostate cell function: role of insulin and IGF1

Obesity is a major health problem that courses with severe comorbidities and a drastic impairment of homeostasis and function of several organs, including the prostate gland (PG). The endocrine–metabolic regulatory axis comprising growth hormone (GH), insulin and IGF1, which is drastically altered under extreme metabolic conditions such as obesity, also plays relevant roles in the development, modulation and homeostasis of the PG. However, its implication in the pathophysiological interplay between obesity and prostate function is still to be elucidated. To explore this association, we used a high fat–diet obese mouse model, as well as in vitro primary cultures of normal‐mouse PG cells and human prostate cancer cell lines. This approach revealed that most of the components of the GH/insulin/IGF1 regulatory axis are present in PGs, where their expression pattern is altered under obesity conditions and after an acute insulin treatment (e.g. Igfbp3), which might have some pathophysiological implications. Moreover, our results demonstrate, for the first time, that the PG becomes severely insulin resistant under diet‐induced obesity in mice. Finally, use of in vitro approaches served to confirm and expand the conception that insulin and IGF1 play a direct, relevant role in the control of normal and pathological PG cell function. Altogether, these results uncover a fine, germane crosstalk between the endocrine–metabolic status and the development and homeostasis of the PG, wherein key components of the GH, insulin and IGF1 axes could play a relevant pathophysiological role.

β-Adrenergic Receptor Subtypes in the Urinary Tract

Within the urinary tract, β-adrenergic receptors (AR) are found largely on smooth muscle cells but are also present, at least in the bladder, in the urothelium and on afferent nerves. Our understanding of β-AR subtype expression and function is hampered by a lack of well-validated tools, particularly with regard to β(3)-AR. Moreover, the β-AR subtypes involved in a specific function may differ between species. In the ureter, β-AR can modulate pacemaker activity and smooth muscle tone involving multiple subtypes. In the human bladder, β-AR promote urine storage. Bladder smooth muscle relaxation primarily involves β(3)-AR, and the agonists selective for this subtype are in clinical development to treat bladder dysfunction. While prostate and urethra also express β-AR, the overall physiological role in these tissues remains unclear.

Muscarinic receptors and their mRNAs in type 2 Goto-Kakizaki diabetic rat prostate

BACKGROUND

As increasing evidence is pointing towards the relationship between diabetes and benign prostatic hyperplasia/lower urinary tract symptoms, we investigated the pharmacological properties and gene expressions of the muscarinic receptors in type 2 diabetes rat prostate.

METHODS

Twelve- and 70-week-old male Goto-Kakizaki (GK) rats and age-matched male Wistar rats were used in this study. The densities of muscarinic receptors (B(max) values) were determined by saturation studies with [(3)H]NMS ([N-methyl-(3)H] scopolamine methyl chloride) in the prostatic membrane particulates. The participation levels of M(1), M(2), and M(3) receptor protein and mRNA levels in the prostate were investigated by immunoblot analysis and real-time polymerase chain reaction (PCR), respectively.

RESULTS

The B(max) values in 12-week-old Wistar and GK, and in 70-week-old Wistar and GK rat prostates were 36.0 +/- 2.8, 49.4 +/- 11.4, 22.0 +/- 2.2, and 47.0 +/- 4.1 fmol/mg protein, respectively. However, there were no significant differences in the affinity constants between any groups. Immunoblot analysis showed the existence of significant amounts of M(1), M(2), and M(3) receptor subtypes in each rat prostate. According to real-time PCR studies the rank order of expression levels of muscarinic receptors mRNA subtypes in the prostate were M(3) > M(2) > M(1). In each receptor subtype in each group, diabetes induced up-regulation of mRNAs while the advanced age of the rats was related with down-regulation of mRNAs.

CONCLUSIONS

Our data indicated that type 2 diabetes induced up-regulation and age-related down-regulation of the expressions of muscarinic receptors and their mRNAs in the rat prostate.

Studying noninvasive indices of vagal control: the need for respiratory control and the problem of target specificity

Respiratory sinus arrhythmia (RSA) is a popular index of cardiac vagal control; however, research has rarely adequately addressed respiratory influences on RSA. In addition, simplistic views of the parasympathetic system have resulted in an overinterpretation of RSA as a general indicator of vagal control. Research using a respiration-corrected time-domain index of RSA has yielded plausible findings that substantially deviate from uncorrected RSA. Paced breathing, which is used for baseline calibration of RSA in this correction procedure, allows for a representative sampling of respiratory influences on RSA and has minimal impact on autonomic regulation. Past research has largely focused on cardiac vagal activity and ignored the extent of target specificity in the parasympathetic system. More research is needed on new noninvasive indices of vagal control at other organ sites. Studies also need to address muscarinic receptor sensitivity before noninvasive vagal indices can be interpreted as markers of central vagal outflow.

Alpha1-, alpha2- and beta-adrenoceptors in the urinary bladder, urethra and prostate

1 We have systematically reviewed the presence, functional responses and regulation of alpha(1)-, alpha(2)- and beta-adrenoceptors in the bladder, urethra and prostate, with special emphasis on human tissues and receptor subtypes. 2 Alpha(1)-adrenoceptors are only poorly expressed and play a limited functional role in the detrusor. Alpha(1)-adrenoceptors, particularly their alpha(1A)-subtype, show a more pronounced expression and promote contraction of the bladder neck, urethra and prostate to enhance bladder outlet resistance, particularly in elderly men with enlarged prostates. Alpha(1)-adrenoceptor agonists are important in the treatment of symptoms of benign prostatic hyperplasia, but their beneficial effects may involve receptors within and outside the prostate. 3 Alpha(2)-adrenoceptors, mainly their alpha(2A)-subtype, are expressed in bladder, urethra and prostate. They mediate pre-junctional inhibition of neurotransmitter release and also a weak contractile effect in the urethra of some species, but not humans. Their overall post-junctional function in the lower urinary tract remains largely unclear. 4 Beta-adrenoceptors mediate relaxation of smooth muscle in the bladder, urethra and prostate. The available tools have limited the unequivocal identification of receptor subtypes at the protein and functional levels, but it appears that the beta(3)- and beta(2)-subtypes are important in the human bladder and urethra, respectively. Beta(3)-adrenoceptor agonists are promising drug candidates for the treatment of the overactive bladder. 5 We propose that the overall function of adrenoceptors in the lower urinary tract is to promote urinary continence. Further elucidation of the functional roles of their subtypes will help a better understanding of voiding dysfunction and its treatment.

Effect of insulin treatment on tissue size of the genitourinary tract in BB rats with spontaneously developed and streptozotocin-induced diabetes

To examine the differences between spontaneous and streptozotocin (STZ)-induced diabetes, four parallel studies were performed; three studies of diabetes-prone BB (BBDP/Wor) rats maintained for 8, 16, and 32 weeks and one study of STZ-injected diabetes-resistant BB (BBDR/Wor) rats maintained for 32 weeks. Each diabetic study has three groups of rats: a control group; a euglycemic group, which received sufficient amounts of insulin; and a hyperglycemic group, which received a suboptimal dose of insulin. The extent of tissue weight changes was generally shown to be less dramatic in the euglycemic diabetic than in the hyperglycemic diabetic rats. STZ-induced diabetes increased the bladder weight more dramatically (up to 3-fold) than did spontaneous diabetes (up to 2-fold). Furthermore, a significant decrease in the size of the adrenal gland (20%) and testis (10%) is observed only with spontaneous diabetes, whereas a significant decrease in the size of the ventral prostate (30%) is observed only with STZ-induced diabetes, although the serum testosterone levels are similar in both groups. Our data demonstrate that there are differences in the effect of insulin treatment on the tissue size of the genitourinary tract between spontaneously developed and streptozotocin-induced diabetes in BB rats.

Regulatory effect of castration on endothelins, their receptors and endothelin-converting enzyme in rat seminal vesicle

OBJECTIVE

To investigate the effects of castration on the expression of endothelins (ETs), ET receptors and ET converting enzyme-1 (ECE-1) in the rat seminal vesicle (RSV).

MATERIALS AND METHODS

Sprague-Dawley rats (3 months old) were surgically castrated or sham-operated, and then killed 7 days after surgery. Biochemical and pharmacological properties and the location of ET receptors in the RSV were determined by a series of binding experiments with [125I]ET-1, using membrane particulates and slide-mounted frozen sections of RSV. Expression levels of ETA and ETB receptor subtypes, ET-1, ET-3 and ECE-1 mRNAs were assessed by relative multiplex reverse-transcription polymerase chain reaction (RT-PCR).

RESULTS

The density of total ET receptors increased significantly in the seminal vesicle of the castrated rat. The predominance of the ETA receptor subtype in the RSV did not change with castration. Autoradiographic studies showed the presence of ET receptors on the smooth muscle and epithelium of the RSV. In addition, RT-PCR showed an up-regulation in the expression of ETA and ETB receptor subtypes, ET-1 and ECE-1 mRNAs in the seminal vesicle of the castrated rat. However, castration caused no significant change in the expression levels of ET-3 mRNA.

CONCLUSION

These findings suggest a regulatory role for testosterone in the expression of the ET receptor system in the RSV.

Cholinergic innervation and function in the prostate gland

The mammalian prostate is densely innervated by hypogastric and pelvic nerves that play an important role in regulating the growth and function of the gland. While there has been much interest in the role of the noradrenergic innervation and adrenoceptors in prostate function, the role of cholinergic neurones in prostate physiology and pathophysiology is not well understood. This review focuses on the role of acetylcholine and cholinoceptors in prostate function. Nitric oxide, vasoactive intestinal polypeptide, and/or neuropeptide Y are co-localised with cholinesterase and/or acetylcholine transporter in some of the nerve fibres supplying the prostate. Their roles are also briefly discussed in this review. A dense network of cholinesterase-staining fibres supplies both prostate epithelium and stroma, suggesting a role of acetylcholine and/or co-localised neuropeptides in the modulation of prostatic secretions, as well as smooth muscle tone. A predominantly epithelial location for prostate muscarinic receptors indicated a major secretomotor role for acetylcholine. The muscarinic receptor subtype mediating muscarinic agonist-induced smooth muscle contraction or enhancement of contractions evoked by nerve stimulation differs in different species. In the human, there is evidence for M(1) receptors on the epithelium, M(2) receptors on the stroma, and both M(1) and M(3) receptors in some prostate cancer cell lines. Several recent investigations indicate that muscarinic receptors may also mediate or modulate normal, benign, and malignant prostate growth. The role of muscarinic agonists and their receptors and the influences of age, testicular, and other steroids in regulating the effects are reviewed.

Protein kinase C and the sub-sensitivity and sub-reactivity of the diabetic rat prostate gland to noradrenaline

Concentration-response curves to noradrenaline (1 nM-100 microM) were obtained in prostates from 6-week streptozotocin diabetic, insulin-treated diabetic or control rats. Compared to the curve obtained in controls, those obtained in prostates from diabetic and insulin-treated diabetic rats were shifted rightward. The alpha1-adrenoceptor antagonist, prazosin (100 nM), caused a rightward shift of the curves in prostates from all groups. In contrast, the uptake 1 inhibitor, nisoxetine (300 nM), only produced a leftward shift of the curves in prostates from control and insulin-treated diabetic rats. However, frequency-response curves obtained in prostates from both control and diabetic rats were shifted leftward by nisoxetine (300 nM). The concentration-response curve to the alpha1-adrenoceptor agonist, methoxamine (10 nM-100 microM), obtained in prostates from diabetic rats was shifted rightward compared with controls. Calphostin C (500 nM), a protein kinase C inhibitor, caused a leftward shift of the curve in prostates from diabetic, but not control, rats. The protein kinase C inhibitor, bisindolylmaleimide I (500 nM), beta-adrenoceptor antagonist, propranolol (500 nM) and muscarinic cholinoceptor antagonist, atropine (300 nM), had no effect on the noradrenaline concentration-response curves of prostates from control or diabetic rats. Our results suggest that diabetes reduces the sensitivity and reactivity of the prostate to noradrenaline-induced stimulation, and this reduction may be due to changes in protein kinase C activity.

Beta2-adrenoceptor-mediated inhibition of field stimulation induced contractile responses of the smooth muscle of the rat prostate gland

Isolated preparations of rat prostate responded to electrical field stimulation (2 strains every 60 s, 0.5 ms, 10 Hz, 80 V) with contractions. The adrenoceptor agonists adrenaline, isoprenaline and noradrenaline (0.1 nM(-10) x microM) elicited concentration-dependent inhibition of electrical field stimulation-induced contractions of the rat prostate. Phenylephrine had no effect on the amplitude of electrical field stimulation-induced contractions. The rank order of potency was isoprenaline> or =adrenaline=noradrenaline>phenylephrine. Inhibition of electrical field stimulation-induced contractions by isoprenaline was attenuated by propranolol (1 microM). The selective beta1-adrenoceptor agonist (-)-1-(3,4-dimethoxy-phenethylamino)-3-(3,4-dihydroxyphenoxy)-2-propanol)oxalate (RO363) and the selective beta2-adrenoceptor agonist salbutamol (1 nM(-100) x microM) were approximately equipotent in inhibiting electrical field stimulation-induced contractions but the selective beta3-adrenoceptor agonist sodium 4-(2-[2-hydroxy-[3-chlorophenyl]ethylamino]propyl)phenoxyacetate (BRL 37344, 1 nM(-100) x microM) did not inhibit electrical field stimulation-induced contractions. The selective beta2-adrenoceptor antagonist, (+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol (ICI 118 551, 0.1 microM) attenuated inhibitory responses to isoprenaline and salbutamol, while the selective beta1-adrenoceptor antagonist atenolol (3 microM) did not. Contractions induced by electrical field stimulation were also inhibited by forskolin (10 nM(-3) x mM) but unaffected by sodium nitroprusside (10 nM(-1) x mM) indicating the presence of an inhibitory cAMP mechanism. These data suggest that stimulation of beta2-adrenoceptors can inhibit contractions of the rat prostate induced by electrical field stimulation.

Expression of endothelin receptor subtypes and their messenger RNAs in diabetic rat prostate: effect of insulin treatment

Streptozotocin (STZ)-induced diabetes causes an upregulation in the expression of endothelin (ET) receptors in the rat prostate (Eur J Pharmacol 310:197, 1996). We examined the effects of insulin treatment, started 8 weeks after the induction of diabetes, on the expression and distribution of ET receptors and their respective mRNAs in the rat prostate. The densities, pharmacological properties and distribution of ET receptors in the rat prostate were examined using radioligand receptor binding and autoradiographic studies, and gene expression of ET receptors was evaluated utilizing the reverse transcription-polymerase chain reaction (RT-PCR). STZ-injected rats had smaller prostates and reduced serum testosterone levels than control and insulin treated diabetic animals. ET receptor density was shown to be significantly higher in the prostate from diabetic rats than those from either control or insulin treated diabetic animals. The pharmacological profile of prostatic ET receptors was similar in all groups (approximately 80% ET(A); 20% ET(B) subtype). ET receptors were predominantly localized to the prostatic stroma. Induction of diabetes increased the expression of mRNA levels of ET(A) and ET receptors, and insulin treatment reversed this upregulation to control levels. These results indicate that (1) ET receptor subtypes are expressed in the rat prostate as transcription and translation products; (2) insulin can normalize the diabetes-induced upregulation in the expression of ET receptors and their respective mRNAs; and (3) diabetes-induced regression of the prostate may involve an alteration in ET receptors.

Expression and localization of basic fibroblast growth factor in diabetic rat prostate

OBJECTIVE

To assess fibroblast growth factor-2 (FGF2/bFGF), which is important in the development and maintenance of the normal prostate and in the development of human benign prostatic hyperplasia (BPH) and prostatic carcinoma, in an animal model of experimentally induced diabetes. Materials and methods Using Western blotting and immunohistochemical analyses, the expression of FGF2 in prostates from several groups of rats was investigated. Rats had diabetes for 8 or 16 weeks (induced by intravenous injection with 65 mg/kg streptozotocin); rats were also treated with insulin (starting 8 weeks after the induction of diabetes, for 8 weeks), and two further groups acted as age-matched control rats. Immunohistochemical markers for smooth muscle (alpha-actin) and epithelium (cytokeratin) were used to distinguish different cell types in adjacent prostatic sections.

RESULTS

Diabetic rats had smaller prostates and lower serum testosterone levels than their controls; insulin treatment of diabetic rats increased prostatic size and testosterone levels. As shown by Western blotting, diabetes caused greater FGF2 expression than in controls, whereas reverse-transcriptase polymerase chain reaction studies showed similar levels of prostatic FGF-2 mRNA in all groups. Immuno-histochemical studies showed that FGF-2 was expressed in both stromal and epithelial components of the rat prostate. Furthermore, although the expression of FGF2 was higher in epithelial than stromal cells in control prostates, it was distributed uniformly in the diabetic prostate.

CONCLUSION

The differences in the level of expression and pattern of distribution of FGF2 suggests a potential role for FGF2 in the changes observed in prostatic growth in diabetic rats.

Effects of insulin treatment on diabetes-induced alterations in endothelin receptors in rat ureter

BACKGROUND

The present investigation was undertaken to examine the effect of insulin treatment on diabetes-induced alterations in endothelin (ET) receptors in rat ureters.

METHODS

The biochemical properties of ET receptors were examined in rat ureters from the following groups: 8 weeks diabetic (D8); 8 weeks age-matched control (C8); 16 weeks diabetic (D16); 16 weeks diabetic-insulin treated (insulin started 8 weeks after the onset of diabetes) (DI16); and 16 weeks age-matched control (C16). Diabetes was induced by the i.v. injection of 65 mg/kg streptozotocin (STZ).

RESULTS

The densities of ET receptors (Bmax values), as determined by saturation experiments with [125I]-ET-1, in the ureteral plasma membranes of D8, C8, D16, DI16 and C16 were 91.7 +/- 10.1, 42.1 +/- 7.2, 71.1 +/- 2.4, 51.5 +/- 6.3 and 45.1 +/- 3.3 fmol/mg of protein, respectively. [125I]-ET-1 binding to the ET receptors in rat ureteral membrane particulates was inhibited by ET-1 (non-selective), ET-3 (ET(B/C selective), BQ610 (ET(A) selective) and IRL 1620 (ET(B) selective) with the following rank order of Ki values: ET-1 < BQ 610 < ET-3 << IRL 1620. The pharmacological profile of the ET receptors was similar in all groups examined and was consistent with the predominance of the ET(A) receptor subtype in the ureteral membrane particulates. The subtype specificity of ET receptors in the ureteral tissues is confirmed with inhibition data obtained from similar binding studies in cloned human ET(A) and ET(B) receptors.

CONCLUSION

The data indicate that diabetes results in an up-regulation of ET receptors in the rat ureter, which is normalized by insulin treatment.

Effect of experimental diabetes on rat prostate endothelin receptors

We studied the properties of endothelin receptors in the prostate of 8-week streptozotocin-diabetic and control rats. The density of endothelin receptors, as determined by saturation experiments with [125I]endothelin-1, were 95.8 +/- 5.4 and 171.3 +/- 16.7 fmol/mg of protein in control and diabetic rat prostates, respectively. The pharmacological profile of the endothelin receptors was similar in both groups and was consistent with the predominance of the endothelin ETA receptor subtype in the prostate. Thus, the induction of diabetes upregulates the expression of endothelin receptors in the rat prostate, but does not alter the pharmacological profile of the receptors in these tissues.

Diabetic sexual dysfunction

Although the overall incidence of erectile dysfunction in the general population between the ages of 40 and 70 years is 52%, men with diabetes mellitus have impotence at an earlier age and with a significantly higher prevalence, ranging as high as 75%. Numerous advances have been made in understanding the physiologic and biochemical mechanisms controlling penile erection. Improved clinical techniques for the diagnosis and treatment of impotence, including dynamic vascular testing, intracavernosal pharmacotherapy, and microsurgical revascularization, have allowed us to enter a new and exciting era in the quest for a more complete understanding of erectile dysfunction.

Characterization of muscarinic cholinoceptor in primary culture of smooth muscle cells from human prostate

We obtained a primary culture of prostatic cells by an explant method from patients with benign prostatic hypertrophy (BPH). Ultrastructural morphology and growth characteristics of these cells conformed to those reported for smooth muscle cells isolated from vascular and visceral tissue sources. The cells retained their original character including the presence of androgen receptor, acid phosphatase and normal chromosomal number. [3H]-methyl-quinuclidinyl benzilate (QNB) saturation experiments showed the existence of a homogeneous population of binding sites with a high affinity and low capacity (KD = 0.17 +/- 0.05 nM., Bmax = 15,000 sites per cell). Inhibition of [3H]-methyl-QNB binding by nonlabelled compounds showed these [3H]-methyl-QNB binding sites to be M2 muscarinic cholinoceptors. cAMP formation induced by forskolin and isoproterenol was inhibited by carbamoyl choline and oxotremorine. These results suggest that prostatic smooth muscle cells contain M2 muscarinic cholinoceptors and that these cholinoceptors couple adenylate cyclase inhibition.

Diabetes-induced alterations in the properties of muscarinic cholinergic receptors in rat vas deferens

Muscarinic cholinergic receptors were identified and characterized by radioligand receptor binding assay using [3H]quinuclidinyl benzilate (QNB) in rat vas deferens membrane particulates of three experimental groups: 1) 8-week diabetic, 2) 8-week diabetic insulin-treated and 3) age-matched control. Diabetes was induced by the intravenous injection of 65 mg./kg. streptozotocin (STZ). The density of muscarinic receptors (Bmax values), as determined by saturation experiments with [3H]QNB, was demonstrated to be higher in the vas deferens of diabetic rats than in the vas deferens of control and diabetic insulin-treated rats. The equilibrium dissociation constants (KD values), however, were similar in all three groups. Muscarinic cholinergic antagonists competed with [3H]QNB binding sites in the vas deferens membrane particulates with the following rank order of Ki values: atropine < methoctramine < or = 4-DAMP < AF-DX 116 < HHSiD < pirenzepine = pfHHSiD. The pharmacological profile of muscarinic receptors was similar in all three groups. Additional pharmacological studies showed a similar rank order of Ki values for vas deferens, bladder dome and heart, but this rank order was significantly different in cerebral cortex and prostate. This is consistent with the predominance of the M2 muscarinic cholinergic receptor subtype in the rat vas deferens. It is concluded that STZ-induced diabetes causes an upregulation of muscarinic cholinergic receptor density in the rat vas deferens that can be prevented by the administration of insulin.