Alpha1-adrenoceptors in testosterone-induced prostatic hypertrophy

Testosterone regulates smooth muscle contractile pathways in the rat prostate: emphasis on PDE5 signaling

Testosterone (T) plays a permissive role in the development of benign prostatic hyperplasia (BPH), and phosphodiesterase 5 inhibitors (PDE5is) have been found to be effective for BPH and lower urinary tract symptoms (LUTS) in clinical trials. This study investigated the effect of T on smooth muscle (SM) contractile and regulatory signaling pathways, including PDE5 expression and functional activity in prostate in male rats (sham-operated, surgically castrated, and castrated with T supplementation). In vitro organ bath studies, real-time RT-PCR, Western blot analysis, and immunohistochemistry were performed. Castration heavily attenuated contractility, including sensitivity to phenylephrine with SM myosin immunostaining revealing a disrupted SM cell arrangement in the stroma. PDE5 was immunolocalized exclusively in the prostate stroma, and orchiectomy signficantly reduced PDE5 immunopositivity, mRNA, and protein expression, along with nNOS and ROKβ mRNA, whereas it increased eNOS plus α(1a) and α(1b) adrenoreceptor expression in castrated animals. The PDE5i zaprinast significantly increased prostate strip relaxation to the nitric oxide donor sodium nitroprusside (SNP) in control but not castrated rats. But SNP alone was more effective on castrated rats, comparable with sham treated with SNP plus zaprinast. T supplementation prevented or restored all above changes, including SNP and zaprinast in vitro responsiveness. In conclusion, our data show that T positively regulates PDE5 expression and functional activities in prostate, and T ablation not only suppresses prostate size but also reduces prostatic SM contractility, with several potential SM contraction/relaxation pathways implicated. Zaprinast findings strongly suggest a major role for PDE5/cGMP in this signaling cascade. PDE5 inhibition may represent a novel mechanism for treatment of BPH.

Inhibition of Testosterone-Induced Hyperplasia of the Prostate of Sprague-Dawley Rats by Pumpkin Seed Oil

The oil from the pumpkin (Cucurbita pepo) seed is claimed to be useful in the management of benign prostatic hyperplasia. This investigation seeks to examine the effect of pumpkin seed oil on testosterone-induced hyperplasia of the prostate of rats. Hyperplasia was induced by subcutaneous administration of testosterone (0.3 mg/100 g of body weight) for 20 days. Simultaneous oral administration of either pumpkin seed oil (2.0 and 4.0 mg/100 g of body weight) or corn oil (vehicle) was also given for 20 days. The weights of the rats were recorded weekly, and the influence of testosterone and pumpkin seed oil on the weight gain of the rats was examined. On day 21, rats were sacrificed, and the prostate was removed, cleaned, and weighed. The prostate size ratio (prostate weight/rat body weight) was then calculated. Neither testosterone nor pumpkin seed oil had any significant influence on the weight gain of the rats. Testosterone significantly increased prostate size ratio (P < .05), and this induced increase was inhibited in rats fed with pumpkin seed oil at 2.0 mg/100 g of body weight. The protective effect of pumpkin seed oil was significant at the higher pumpkin seed oil dose (P < .02). We conclude pumpkin seed oil can inhibit testosterone-induced hyperplasia of the prostate and therefore may be beneficial in the management of benign prostatic hyperplasia.

The role of the alpha-1 adrenoceptor in modulating human mesangial cell matrix production

BACKGROUND

The sympathetic nervous system is frequently activated in hypertension and may modify various aspects of renal function. Whether modulation of the sympathetic nervous system directly influences the development of renal fibrosis is yet to be established. The current study investigates the role of the alpha-1 adrenoceptor on human mesangial cell scarring.

METHODS

Human mesangial cells were injured with macrophage-conditioned medium (MPCM) and treated with doxazosin for 1 or 3 days.

RESULTS

alpha-1 Adrenoceptor antagonist doxazosin of 2 micromol/l reduced fibronectin protein in MPCM-injured female mesangial cells by 31 +/- 1.03% (P < 0.001) and by 9.5 +/- 0.3% (P = 0.01) in male mesangial cells. The differential response between sexes was significant (P = 0.004). alpha-1B Adrenoceptors were detected in human mesangial cells by reverse transcription-polymerase chain reaction with expression in female cells being 87% higher than in males (P = 0.04). Injury with MPCM reduced alpha-1B adrenoceptor mRNA expression in both cell types. Doxazosin had no effect on the protein levels of transforming growth factor-beta (TGF-beta) or interleukin-1beta (IL-1beta), however, a small reduction in tumour necrosis factor-alpha (TNF-alpha) levels was observed. Doxazosin had no effect on the modulators of matrix turnover matrix metalloproteinases MMP3, MMP9 and tissue inhibitor of matrix metalloproteinases (TIMP-1), although a significant reduction in tissue plasminogen activator (tPA); (36.5 +/- 2.6%, P < 0.001) was observed. Doxazosin caused an up-regulation of kallikrein expression, both at mRNA and protein levels. Co-treatment with the bradykinin B2 receptor antagonist HOE140 was able to attenuate the effects of doxazosin treatment on fibronectin levels.

CONCLUSION

These data suggest that inhibition of alpha-1B adrenoceptors in mesangial cells exerts an anti-fibrotic effect in a sex-specific manner via modulation of the kallikrein-kinin/plasminogen activator system.

Effects of androgen manipulation on α1-adrenoceptor subtypes in the rat seminal vesicle

This study analyses possible changes during surgical and chemical castration in the expression and pharmacological characteristics of alpha1-adrenoceptor in adult rat seminal vesicle. Ribonuclease protection assays indicated that alpha1a--was the predominant mRNA, while alpha1b-and alpha1d-adrenoceptor transcripts were detected in lower abundance in this tissue. alpha1a-adrenoceptor mRNA expression presented a complex dependency on androgens, while alpha1b- and alpha1d-adrenoceptor transcripts were both upregulated with surgical and chemical castration, suggesting a negative modulation by androgens. Testosterone treatment reversed the effects caused by surgical castration. Functional studies confirmed the involvement of alpha1A- and alpha1B-adrenoceptor in the seminal vesicle contractile responses, and suggested that alpha1B-induced contractile response was upregulated after castration. Taken together, the results suggest that alpha1-adrenoceptor expression in seminal vesicle is differentially regulated by the androgen status of the rat.

Alpha1-adrenoceptor subtypes in rat epididymis and the effects of sexual maturation

We have characterized the expression of alpha1-adrenoceptor in epididymis from rats in different stages of sexual maturation: 40 (immature), 60 (young adult), and 120 (adult) days of age. Plasma testosterone levels were low in the immature animals but increased significantly in the 60- and 120-day-old animals. These changes were followed by a progressive increase in rat body weight and in caput and cauda epididymis relative weight. Reverse transcription polymerase chain reaction assay indicated that alpha1a-, alpha1b-, and alpha1d-adrenoceptor transcripts were present in both caput and cauda epididymis from adult rats. Ribonuclease protection assays further indicated that the expression of these alpha1-adrenoceptor transcripts differed with age and epididymal region analyzed. Prazosin (nonselective alpha1 antagonist), 5-methyl urapidil (alpha1A-selective), and BMY 7378 (alpha1D-selective) displaced [3H]prazosin binding curves in caput and cauda epididymis from 40- and 120-day-old rats. The potency order for these antagonists, as calculated from the negative logarithm of the inhibition constant (pK(i)) values for the high-affinity sites, indicated a predominant population of alpha1A-adrenoceptor subtype in caput and cauda epididymis from adult animals. Differences in pK(i) values in caput and cauda epididymis from immature and adult animals also suggested that the relative amount of alpha1-adrenoceptors, at the protein level, is modulated by sexual maturation. Taken together, the changes in alpha1-adrenoceptor expression during sexual maturation may suggest specific roles for these receptors in epididymal function.

Effects of castration on contraction and alpha(1)-adrenoceptor expression in rat prostate

1. The prostate function is regulated by androgens and alpha-adrenergic activity. Clinically, antiandrogens and/or alpha(1)-adrenergic antagonists are commonly used to treat symptomatic prostatic hypertrophy. To elucidate the effects of androgen deprivation on prostate contractility via alpha(1)-adrenoceptor, the characteristics and expression of alpha(1)-adrenoceptors were examined in castrated rats. 2. Isolated prostate strips from intact and castrated rats were subjected to a phenylephrine stimulated contraction. Prazosin (10 nM), [(3)H]-prazosin and phenoxybenzamine (3 - 300 nM) were used for inhibition assay, receptor characterization and partial alkylation of alpha-adrenoceptor, respectively. The mRNA content of three subtypes of alpha-adrenoceptors was determined by reverse transcription combined with polymerase chain reaction (RT - PCR). 3. Contractile response to phenylephrine increased in castrated rats, which could be explained by a relative increase of the stromal component. A lowered contraction potency was also noted in castrated rats. Receptor binding assay indicated minimal changes in the affinity or density of alpha(1)-adrenoceptor. Escalating alkylation of the alpha(1)-adrenoceptor population resulted in a rightward shift in the contraction-response curves before depressing maximal contractile force, and the suppression was detected at lower doses in castrated rats. RT - PCR study confirmed the expression of three types of alpha(1)-adrenoceptor, alpha(1a), alpha(1b) and alpha(1d)-adrenoceptors, in intact rat prostate, and revealed that alpha(1a)-adrenoceptor, but not alpha(1b) or alpha(1d)-adrenoceptors, was down-regulated in castrates. 4. The results show that androgen deprivation suppressed alpha(1)-adrenergic contractility of rat prostate strips, and the suppression was associated with down-regulation of receptor reserve for the alpha(1a)-adreneroceptor population expressed in intact rat prostate.