Predominant epithelial localization of type A gamma-aminobutyric acid receptor sites within rat seminal vesicles and prostate glands.

In order to understand the role of the gamma-aminobutyric acid (GABA)-ergic system in the reproductive organs of the male, the biochemical characteristics and the autoradiographic localization of GABA type A (GABAA) receptor sites were studied in sections of the rat epididymis, seminal vesicles and prostate gland (lateral lobe) using 3H-muscimol as a ligand. No specific 3H-muscimol binding occurred in the epididymis. 3H-muscimol was bound to sections of seminal vesicles and prostate glands in a manner consistent with the labeling of specific GABAA receptors. Binding was saturable, reversible, with Kd values of 27.5 +/- 2.0 and 26.0 +/- 1.9 nmol/l and Bmax values of 230 +/- 21 and 160 +/- 13 fmol/mg protein for seminal vesicles and prostate glands, respectively. The rank order of potency of GABAergic drugs in inhibiting 3H-muscimol binding to sections of seminal vesicles and prostate glands was also consistent with the labeling of GABAA receptors. Autoradiography demonstrated the predominant accumulation of silver grains in the epithelium of seminal vesicles and prostatic glandular tissue. These findings further support the suggestion of a possible role of GABA in the male reproductive function. The predominant epithelial localization of GABAA receptors in the seminal vesicles and in the prostate gland allows us to hypothesize that GABA may be involved in the secretory activities of these glands.