Modulation of alpha 1-adrenoceptors and functional consequences in the bisected rat vas deferens following chronic inhibition of neuronal noradrenaline uptake

The androgenic effect of norethisterone and 5alpha-norethisterone on the contractile response of the rat vas deferens to methoxamine and serotonin

Norethisterone (NET) and its metabolite 5alpha-norethisterone (5alpha-NET) are competitors for the androgen receptor. The sensitivity of the rat vas deferens to the contractile action of methoxamine and serotonin is regulated by hormonal and anatomical factors. The aim of this study was to evaluate the ability of NET and 5alpha-NET to induce the androgen-regulated contractile response to methoxamine and serotonin in the epididymal and prostatic portions of rat vas deferens. Adult male rats either intact, castrated or steroid-treated castrated were used. The contractility was recorded isometrically, and non-cumulative concentration-response curves to either methoxamine or serotonin were obtained. NET and 5alpha-NET partially restored the sensitivity to methoxamine and serotonin in the epididymal portion of castrated rats. The maximal responses to both agonists were significantly higher than those observed in castrated rats, and significantly lower than the responses observed in either intact or androgen-treated castrated rats. The prostatic portion was less responsive to both agonists than the epididymal portion, in all groups but castrated rats, as castration induced sensitivity to both agonists. NET and 5alpha-NET displayed a partial though similar androgenic activity in the rat vas deferens. These results contrast with previous reports where a decrease of androgenic effect due to the 5alpha-reduction of NET has been found.

Alpha-1 adrenoceptor subtypes (high, low) in human benign prostatic hypertrophy tissue according to the affinities for prazosin

BACKGROUND

A novel classification of alpha-1 adrenoceptor subtypes (High, Low) was applied to human benign prostatic hypertrophy (BPH) tissue.

METHODS

Human BPH specimens were examined by a radioligand binding assay method using 3H-prazosin, and those data were compared with preoperative therapies.

RESULTS

(1) Scatchard analysis showed a high-affinity site (Kd:27.18 +/- 6.41 pM; Bmax:9.29 +/- 0.98 fM/mg protein; mean +/- SE) as alpha 1H, and a low-affinity site (Kd: 4088.0 +/- 744.34 pM, Bmax: 140.81 +/- 19.98 fM/mg protein) as alpha 1L subtype, for prazosin. (2) The Kd and Bmax were not different in the nontreated group (n = 5), alpha 1 blocker group (n = 5), and antiandrogen group (n = 5), in either alpha 1-high affinity or alpha 1-low affinity subtype. (3) Phenoxybenzamine had different pKi values for the above two adrenoceptor subtypes. Scatchard analysis showed that alpha 1-high affinity binding site disappeared in the presence of 1 microM of phenoxybenzamine, and the Kd and Bmax values in the presence of 1 microM of phenoxybenzamine were almost identical to the alpha 1-low affinity site of the two subtypes.

CONCLUSIONS

Human BPH tissue possesses both alpha 1H- and alpha 1L-adrenoceptor subtypes according to the affinities for prazosin, and only the alpha 1H subtype can be completely inhibited by some concentration of phenoxybenzamine. Treatment by alpha 1 blocker may not change the conditions of alpha 1-adrenoceptors in prostatic tissue.

The human vas deferens: correlation of response pattern to noradrenaline and histological structure

Specimens of human vas deferens were studied histologically and by measuring changes in response to adrenoceptor agonists. In intact tissues noradrenaline induced both lengthening and shortening responses which were identified with contractions of circular and longitudinal muscle respectively. The agonists phenylephrine or methoxamine evoked mainly shortening but little lengthening. The tissues were unresponsive to clonidine or isoprenaline. Longitudinal strips but not rings responded reliably to phenylephrine and to caffeine. The lengthening responses of intact specimens to noradrenaline were relatively insensitive to the antagonist phenoxybenzamine. In contrast both shortening and lengthening responses were inhibited by prazosin or phentolamine but not by idazoxan. A physiological function for the predominance of muscle types in different specimens is proposed. A pharmacological selectivity for the muscle types by alpha 1-selective adrenoceptor agonists and by phenoxybenzamine is discussed and the clinical implication considered.