Rabbit testicular contractions: bimodal interaction of prostaglandin E1 with other agonists

Contractions of rabbit testicular capsules in vitro and in vivo in response to prostaglandin F2a, epinephrine, and acetylcholine were measured in the presence of prostaglandin E1 (PGE1). Contractions induced by these agents were markedly inhibited at 10-7 M concentrations of PGE1 in both preparations. Even so, lower levels of PGE1 (10-8 or 10-9 M) potentiated epinephrine- or acetylcholine-induced stimulation of increased tonus in vovo. Epinephrine, PGE1, and PGF2a caused increased tonus and contractions in vitro and in vovo; however, acetylcholine stimulated the testicular capsule much more in vivo than in vitro. The control log dose-response curve for epinephrine stimulation showed a slight decrease in the upper concentration range. Propranolol, a beta-adrenergic blocking agent, more than overcame this decrease and also prevented a theophylline inhibition of epinephrine-induced contraction. Prostaglandin E1's bimodal effect gives it the ability to modulate testicular contractions by increasing stimulation by other agonists in vovo at low concentrations of PGE1 but inhibiting it at higher concentrations. Thus PGE1 is a potential regulator of testicular capsular motility and possibly sperm transport and hemodynamics.