Characterization of beta-adrenergic receptors in dispersed rat testicular interstitial cells

Effects of co-administration of dopamine and vitamin C on ischaemia-reperfusion injury after experimental testicular torsion-detorsion in rats

The objective of this study was to investigate the effects of dopamine as vasodilator, vitamin C as an antioxidant and combined administration of them on ischaemia-reperfusion (I-R) injury following testicular torsion (TT). Thirty adult male rats were divided into six groups each containing five rats. Testicular ischaemia was achieved by twisting the left testis for 4 h. Group 1 was for determination of the basal values. Group 2 had 4 h TT. Group 3 had 4 h TT and was then treated with dopamine. Group 4 had 4 h TT and was then treated with vitamin C. Group 5 had 4 h TT and was then treated with dopamine and vitamin C. Group 6 was designed as a sham operated group. Testicular torsion caused a significant decrease in the percentage of spermatogenesis and seminiferous tubules diameters compared with the control and sham groups. Administration of dopamine, vitamin C and their combination increased above mentioned parameters and decreased serum malondialehyde levels significantly. However, vitamin C had better results than the other treatments (P < 0.05). In conclusion, a potent antioxidant like vitamin C was found to be more effective than increasing blood flow by a vasodilator like dopamine on improving I-R injury following TT.

Effects of the β2 -agonist clenbuterol on testicular steroidogenic acute regulatory protein mRNA expression in adult rats

This study was carried out to investigate the effects of clenbuterol (CLB) on the testicular (steroidogenic acute regulatory, StAR) protein mRNA expression in rats. Thirty adult male rats were administered CLB by gavage daily at the doses of 0.4, 2.0 and 18.5 mg/kg bw for 14 days in the subacute experiment, whereas 20 rats received a single treatment with CLB at the doses of 20 and 40 mg/kg bw in the acute experiment and 20 rats were treated with 0.9% NaCl solution as vehicle groups. Testicular tissues were collected and snap-frozen in liquid nitrogen and stored at -70 °C until use. The levels of StAR mRNA were detected by RT-PCR. The levels of StAR mRNA were markedly increased (P < 0.05) at both dosages of 20 and 40 mg/kg bw but the effects were not dose-dependent and the mRNA levels of StAR were returned to near normal level after 7 days of CLB withdrawal, compared with the control animals. In the subacute experiment, CLB induced a dose-dependent but no statistical significant reduction (P > 0.05) in the expression levels of StAR mRNA, and the mRNA levels were recovered to near normal level in the groups treated with CLB at dosages of 0.4 and 2.0 mg/kg bw/day following a 7-day withdrawal period, compared with the control animals. The mRNA levels of StAR showed a significant decrease in the groups treated with CLB at the dosage of 18.5 mg/kg bw/day (P < 0.05) after a 1- or 7-day withdrawal period with respect to the control animals. These results demonstrated transient stimulative effects of CLB on testicular StAR mRNA levels and inhibitory effects after treatment with CLB for 14 consecutive days.

Innervation and serotoninergic receptors of the testis interact with local action of interleukin-1beta on steroidogenesis

Testosterone secretion by Leydig cells is affected by interleukin-1beta (IL-1beta). The aim of the present study was to investigate whether partial denervation of the testis or local administration of a serotonin (5-HT) receptor antagonist could alter the changes in testicular steoidogenesis induced by IL-1beta. Intratesticular administration of IL-1beta was combined with vasectomy or local injection of ketanserin (5-HT type 2 receptor antagonist) in immature hemicastrated rats and the effect of the interventions on testicular steroidogenesis was studied. One day after treatment with local injection of IL-1beta induced a significant rise in testosterone secretion that could be prevented by vasectomy (that also means transection of the inferior spermatic nerve). In a model in which neither IL-1beta nor ketanserin interfered with steroidogenesis, administration of the receptor antagonist just prior to IL-1beta treatment significantly reduced testosterone secretion. Data indicate interaction between testicular nerves and IL-1beta action and interaction between testicular 5-HT2 receptors and local effect of IL-1beta on testosterone secretion.

Alpha1-and beta2-adrenoceptors in the human liver with mass-forming intrahepatic cholangiocarcinoma: density and coupling to adenylate cyclase and phospholipase C

Besides the regulation of hepatic metabolic pathways in which adrenoceptors are mainly involved, their effect on the second messenger cAMP is thought to be related to the growth and differentiation of neoplastic cells. However, few studies have been done on the status of these structures in the human liver affected by cholangiocarcinoma (CC). Thus, in this study, changes in densities of alpha1- and beta2-adrenoceptors (alpha1-and beta2-ARs) were investigated in membranes of human liver with cholangiocarcinoma, and for comparison, in membranes of non-adjacent non-tumour liver using the potent antagonists [3H]-prazosin and [1I]-iodocyanopindolol (ICYP) respectively. In addition, the activity of membrane-bound phospholipase C (PLC) and adenylate cyclase (AC) was also studied. In CC liver, the density of alpha1-and beta2-ARs was significantly reduced, compared with non-tumour liver tissues (alpha1-ARs: 23.38+/-4.69 vs 80.35+/-10.52, P=0.0002 beta2-ARs: 14.27+/-2.93 vs 33.22+/-4.32 fmol/mg protein, P=0.03), whereas the ligand affinities (KD) remained unchanged. The beta2-selective antagonist ICI 118,551 was about 100 times more potent in inhibiting ICYP binding than the beta1-selective antagonist CGP 20712A; thus, more than 98% of the beta-ARs were of the beta2-subtypes. The AC activity upon stimulants acting on beta-AR (isoprenaline), G-protein (GTP, NaF) and AC (forskolin) was decreased in CC liver. Similarly, noradrenaline-stimulated PLC activity was significantly reduced in tumour tissues. In conclusion, in CC liver the alpha1- and beta2-ARs density was down-regulated and the neoplastic invasion blunted AC and PLC activity. These quantitative changes may help to elucidate not fully understood pathogenetic mechanisms of disturbed hepatic metabolic processes, such as hypoglycemia during cancer in human liver.

In the adult male rhesus monkey (Macaca mulatta), unilateral orchidectomy in the face of unchanging gonadotropin stimulation results in partial compensation of testosterone secretion by the remaining testis

This study examined, in adult monkeys, the role that gonadotropin-independent mechanisms play in compensation of testosterone (T) secretion by the testis that remains after unilateral orchidectomy (UO). We employed a model (testicular clamp), in which endogenous gonadotropin secretion was abolished with a GnRH receptor antagonist, and the gonadotropin drive to the testes was concomitantly replaced with an invariant iv pulsatile infusion of recombinant human LH and FSH (1-min pulse every 2.5 h: LH, 0.08-0.12 IU/kg.pulse; FSH, 0.12-0.32 IU/kg.pulse) that provided the Leydig cells with a physiological stimulus. Within 5 h of UO (n = 5), circulating T concentrations had declined to 43% of pre-UO levels. By d 4, however, loss of the first testis was partially compensated, as reflected by the finding that circulating T had reached a plateau of 67% of the pre-UO level, where it remained for the duration of the study (39 d). That the recovery in circulating T was the result of increased T secretion by the remaining testis was suggested by the finding that the pulsatile pattern and decay of T during the intergonadotropin pulse interval before and after UO were indistinguishable. Interestingly, inhibin B production by the remaining testis also showed a delayed, albeit, minor, compensation (13% on d 10-11; P > 0.05) after loss of the first testis. These results suggest that compensation in T production by the remaining testis after UO in adult monkeys may be achieved in part by a gonadotropin-independent mechanism that probably involves direct neural inputs to the primate testis.

Administration of acetylcholine to the spermatic nerve plexus inhibits testosterone secretion in an in vitro isolated rat testis-nerve plexus system

Strong evidence indicated that spermatic nerves are involved in the regulation of testosterone secretion. Our previous work showed that the inferior spermatic nerves play a more significant role than the superior ones in the regulation of testosterone secretion. However, it is unknown whether traditional neurotransmitters are involved in this regulation. In order to evaluate this point, the present experiments were carried out in an in vitro system where an isolated testis-spermatic nerve plexus preparation was incubated in two separate containers, one for the testis and the other for the nerve plexus and both interconnected by the inferior spermatic nerves. Both tissues were maintained in the same environmental conditions except for the neurotransmitter treatment, applied only to the nerve plexus. Acetylcholine can significantly inhibit the secretion of testosterone until the end of incubation. The present experiments suggest that the secretion of testosterone could be regulated, at least in part, by acetylcholine through the inferior spermatic nerves.

Morphological and quantitative study of the Leydig cells of pigs fed with anabolic doses of clenbuterol

The effects of clenbuterol administered at anabolic doses on the testicular interstitium were studied in 30 pigs allocated to three experimental groups. The diet of two groups was supplemented with clenbuterol (Clb) (1 ppm), but whereas in the Clb+ group the treatment was given until slaughter (treatment period: 3 months), in the Clb- group the clenbuterol was withdrawn 2 weeks before slaughter (treatment period: 2-5 months); in the control group, the pigs were fed without clenbuterol. For histological procedures, a fractional sampling scheme was applied and routine techniques for light and transmission electron microscopy were used. The results of subjective morphology and morphometrics showed slight differences between the treated and the control groups. Conversely, the stereological results identified a prominent hyperplasia of the Leydig cells and ultrastructural analysis of these cells revealed a conspicuous increase in the organelles related to testosterone production, suggesting a functional activation of the interstitial cells in response to the clenbuterol treatment.

Beta2 adrenergic receptors mediate cAMP, tissue-type plasminogen activator and transferrin production in rat Sertoli cells

FSH is the main regulator of Sertoli cell function. Nevertheless, several other effectors such as catecholamines can also stimulate these cells through the adenylyl cyclase transduction pathway. However, the expression of beta adrenergic receptors in Sertoli cells is a subject of controversy. The aim of the present study was to determine if there are physiologically functional beta adrenergic receptors in Sertoli cells and to which subtype(s) they belong. In freshly isolated Sertoli cells, isoproterenol, a non selective beta-adrenergic agonist, was found to stimulate cAMP production and tissue-type plasminogen activator secretion. Specific transcripts for the beta1 and beta2, but not beta3, subtypes were detected by RT-PCR analysis. Beta2 transcripts were the form expressed predominantly in Sertoli cells. Binding experiments carried out on freshly isolated and on cytospined Sertoli cells indicated that in both conditions, [125I]iodocyanopindolol binding was inhibited by a non-selective and a 2 selective antagonist, whereas a beta1 selective antagonist had no effect. Scatchard analysis of beta2 specific inhibition revealed a dissociation constant of 0.3 nM and a receptor density of 14000 sites per cell. In freshly isolated Sertoli cells, we observed that cAMP and tissue-type plasminogen activator were stimulated by isoproterenol and a beta2 selective agonist, but not by beta1 or beta3 selective agonists. Accordingly, the isoproterenol-stimulated tissue-type plasminogen activator responses were abolished by the beta2 selective antagonist only. In cultured Sertoli cells, the trend was the same: tissue-type plasminogen activator and transferrin secretions were increased by isoproterenol and beta2 but not by beta1 or beta3 selective agonists. We conclude that freshly isolated Sertoli cells express beta2 adrenergic receptors which are functionally coupled to adenylyl cyclase and that these characteristics are preserved in cell culture. For the tested parameters, catecholamines and FSH effects were similar, but response magnitudes were systematically lower with beta agonists than with FSH. As norepinephrine is normally present in physiologically-relevant amounts in the interstitial fluid, it can be suspected to play a role in the regulation of Sertoli cell function.

Effects of guanethidine-induced sympathectomy on the spermatogenic and steroidogenic testicular functions of prepubertal to mature rats

Selective chemical sympathectomy of the internal genital organs of prepubertal to mature male Wistar rats was performed by chronic treatment with low doses of guanethidine. Sympathetic denervation caused an increase in intratesticular progesterone levels in prepubertal and early pubertal rats in addition to a decrease in androstenedione and testosterone levels in prepubertal animals, thus indicating a decrease in the conversion of progesterone into androgen, probably by blocking the steroidogenic enzymatic pathway at the 17 alpha-hydroxylase/17, 20 desmolase level. A lower degree of testicular maturation, probably related to reduced androgen activity, was observed in prepubertal and early pubertal sympathectomized rats. Concentration of spermatozoa, on the other hand, was increased in the enlarged cauda epididymidis of late pubertal and mature denervated animals. This result is discussed in terms of the impairment of epididymal mechanisms of seminal emission, fluid resorption and spermatozoal disposal.

The hypophyseal-testicular axis and sex accessory glands following chemical sympathectomy with guanethidine of pre-pubertal to mature rats

Selective chemical sympathectomy of the internal sex organs of prepubertal to mature male Wistar rats was performed by chronic treatment with low doses of guanethidine. Plasma testosterone and luteinizing hormone and the intratesticular level of testosterone were determined. The weight and fructose content of seminal vesicle and ventral prostate were also investigated. The results showed that sympathetic innervation is related to the control of the hypophyseal-testicular axis as well as to the growth and potential secretory activity of the male sex accessory glands.

Inhibitory role of cholinergic agonists on testosterone secretion by purified rat Leydig cells

The effects of cholinometics on basal or hCG-induced testosterone (T) release by Percoll-purified Leydig cells of the rat were studied. Acetylcholine and carbachol as well as nicotine decreased basal and hCG-induced T secretion. The ganglionic nicotine antagonist hexamethonium promoted a partial reversal of the inhibitory effect of nicotine on basal or hCG-stimulated T secretion. Atropine also reduced the inhibitory effect of carbachol on basal or stimulated androgen release. These data indicate that, in short-term incubations, testosterone released by purified Leydig cells is inhibited by nicotinic and muscarinic cholinergic agonists, thus supporting the hypothesis that parasympathetic autonomic system may be involved in the negative regulation of testicular androgen secretion.

A potential role for catecholamines in the development and progression of carcinogen-induced mammary tumors: hormonal control of beta-adrenergic receptors and correlation with tumor growth

In order to gain further knowledge on the beta-adrenergic receptor system in DMBA-induced rat mammary tumors, we have studied the correlation between changes in tumoral beta-adrenergic receptor concentration and distribution, progesterone receptor status and tumor growth after ovariectomy and treatment with various ovarian and adrenal steroids, or induction of hyperprolactinemia. Autoradiographic localization of beta-adrenergic receptors in ovariectomized (OVX) animals shows very weak labeling with [125I]cyanopindolol. In these tumors, the connective tissue is predominant, while the epithelial cell content is very low. Similarly, when direct measurements of [125I]cyanopindolol are performed with membrane preparations, beta-adrenergic receptor concentration is sharply reduced 2-3 weeks following ovariectomy or treatment with LHRH against [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide. This effect on the beta-adrenergic receptor population in the tumor is accompanied by the well known effect of castration on tumor growth and progesterone receptor levels, namely a marked regression of tumor growth and a significant decrease in progesterone receptor concentration. Treatment of OVX rats with 17 beta-estradiol (E2) alone or in combination with progesterone (P) caused a highly significant increase in beta-adrenergic and progesterone receptor levels, as well as tumor growth. A similar sharp increase in the value of the three parameters studied was observed following daily treatment of OVX rats with dehydroepiandrosterone (DHEA) or androst-5-ene-3 beta,17 beta-diol (5-ene-diol). The autoradiographic localization of beta-adrenergic receptors in OVX rats treated with 5-ene-diol showed that the epithelial cells were numerous with a high degree of labeling. On the other hand, treatment of OVX animals with the androgen dihydrotestosterone (DHT) did not produce significant changes in beta-adrenergic receptor levels or tumor growth. Finally, endogenously-induced hyperprolactinemia by implanting three anterior pituitary glands under the kidney capsule of OVX animals resulted in a significant increase in beta-adrenergic and progesterone receptor levels as well as tumor growth. The positive correlation observed between changes in beta-adrenergic receptor concentration, progesterone receptor levels and tumor growth indicates a high sensitivity of the beta-adrenergic receptor population of DMBA-induced rat mammary tumors to the hormonal milieu, and suggests that the beta-adrenergic receptor system may represent a valuable parameter of hormone responsiveness.

Cyclic adenosine monophosphate (cAMP) does not mediate the stimulatory action of norepinephrine on testosterone production by the testis of the golden hamster

The role of cAMP in mediating the stimulatory effects of norepinephrine (NE) on testosterone (T) production by hamster testes in vitro was examined using tissue from both gonadally active and gonadally regressed hamsters. As expected from our previous studies, the NE-induced increase in T accumulation in this system was prevented by alpha-adrenoreceptor antagonist prazosin, but not by beta-adrenoreceptor antagonist propranolol. In incubations of regressed testes from short photoperiod-exposed hamsters, NE stimulated accumulation of cAMP in media and tissue. These effects were prevented by propranolol but not by prazosin. In incubations of active testes from long photoperiod-exposed animals, NE stimulated cAMP in the media but not in the tissue, and potentiated the effect of hCG on the accumulation of cAMP only in tissue. When added to incubations with NE and hCG, propranolol, but not prazosin, reduced cAMP levels in media and tissue. Thus, functional alpha- and beta-adrenoreceptors are present in active and regressed testes and can be activated by NE. NE stimulates cAMP production via its action at the beta-receptors and T production via its action at the alpha-receptors. These results imply that cAMP does not mediate the stimulatory action of NE on T production in hamster testes.

Beta-adrenergic receptors in DMBA-induced rat mammary tumors: correlation with progesterone receptor and tumor growth

In order to gain further knowledge about the potential role of catecholamines in mammary carcinoma, we have used the potent beta-adrenergic antagonist cyanopindolol (CYP) as iodinated ligand to characterize beta-adrenergic receptors in membranes prepared from mammary tumors induced by dimethylbenz(a)anthracene (DMBA) administration in the rat. The binding of [125I]CYP to membrane preparations of DMBA-induced rat mammary tumors is rapid at room temperature, reaching half maximal specific binding at 30 min of incubation. Scatchard analysis of the data indicates that [125I]CYP binds to a single class of high affinity sites (114 +/- 2.1 fmoles/mg protein) at an apparent KD value of 38.0 +/- 0.3 pM. The order of potency of a series of agonists to compete for [125I]CYP binding is consistent with interaction with a beta 2-subtype receptor: zinterol greater than (-)isoproterenol greater than (-)epinephrine much greater than (-)norepinephrine. In addition, the potency of a series of specific beta 1 and beta 2 synthetic compounds to displace [125I]CYP in mammary tumors is similar to their potency in typical beta 2-adrenergic tissues. The binding of [125I]CYP to DMBA-induced rat mammary tumors shows a marked stereoselectivity, the (-)isomers of isoproterenol and propranolol being 150 and 80 times more potent, respectively, than their respective enantiomers. The autoradiographic localization of [125I]CYP performed on frozen sections revealed the presence of specific beta-adrenergic receptors in all the malignant cells. Spontaneous mammary tumors of aging (18-22 months) female rats have high levels of beta-adrenergic receptors. Castration decreased the concentration of [125I]CYP binding sites in DMBA-induced mammary tumors. A close correlation was observed between progressing, static, and regressing tumors after ovariectomy and beta-adrenergic receptor concentration. The presence of beta-adrenergic receptors in mammary tumors as well as the modulation of their level by ovarian hormones provides a mechanism for catecholaminergic influence in mammary cancer tissue.

Characterization and localization of beta-adrenergic receptors in control and cryptorchidized rat testis by in vitro autoradiography

beta-adrenergic receptors were localized and characterized in control and cryptorchidized rats to investigate further their role in testicular function. Slide-mounted cryostat sections were incubated with [125I]cyanopindolol, a specific ligand for beta-adrenergic receptors. The subtypes were characterized by the displacement of [125I]cyanopindolol binding by practolol, which binds preferentially to the beta 1 subtype, and zinterol, which is preferential for beta 2 receptors. Labeling was detected by autoradiography, first by exposing sections to Ultrofilm (LKB) and second by dipping slides in NTB-2 Kodak photographic emulsion. The histologic distribution of receptors was analyzed by counting silver grains overlying the testicular structures. It was found that the vast majority of receptors were of the beta 2-subtype. In intact rats, the greatest density of receptors was found in interstitial cells, with some specific labeling over the seminiferous tubules. However, in cryptorchidized animals, the proportion of beta 2 receptors in tubules that contained mainly Sertoli cells appeared to be markedly increased. The results obtained suggest that catecholamines have multiple sites of action in the testis.

Beta-adrenergic receptors and stimulatory effects of (-) isoproterenol on testosterone production in fetal mouse Leydig cells

Beta-adrenergic receptors were characterized in freshly excised fetal mouse testis using the radioiodinated antagonist iodocyanopindolol (ICYP). [125I]-CYP bound to a single class of high affinity sites with a KD value of 42.2 +/- 7.0 pM. Adrenergic agonists competed for ICYP binding sites with the following order of potency: (-)isoproterenol greater than (-)epinephrine much greater than (-)norepinephrine which is typical for a beta 2-adrenergic receptor. A selective beta 2-receptor antagonist ICI 118-551 showed an approximately 200 fold higher affinity than the beta 1-selective compound, betaxolol. The beta-adrenergic agonist (-)isoproterenol did not or slightly affect testosterone production by freshly isolated fetal Leydig cells. The ability of fetal Leydig cells to respond to (-)isoproterenol increased during culture. This change in responsiveness was not accompanied either by modification of the number of binding sites or by change in the binding affinity. Taken together these data suggest that i) the stimulatory effect of (-)isoproterenol on testosterone production by cultured fetal Leydig cells is mediated through beta 2-adrenergic receptors ii), the inability of freshly Leydig cells to respond to catecholamines is probably due to post receptor events.