Effect of porcine follicular fluid on LH and FSH secretion in rats.

To investigate a mode and a site of action of inhibin on FSH and LH secretion, in vivo and in vitro effects of porcine follicular fluid (PFF) on FSH and LH secretion were studied in male rats. PFF administered i.v. suppressed basal FSH levels for 1-8 hr, but did not alter LH levels. On the contrary, PFF given either 1 or 6 hr in advance, suppressed LH-RH stimulated LH responses as well as LH-RH induced FSH responses. In cultured pituitary cells PFF exerted a partial suppressive effect on LH release. PFF suppressed LH release only under the maximal stimulation with 10(-10) M LH-RH and 0.1 mM 3-isobutyl-1-metylxanthine (IBMX) to a lesser degree compared with uniform and greater suppression on FSH release regardless of the experimental conditions. Above results showed a selective suppressive effect of PFF on FSH release and synthesis with a less inhibitory effect on LH release mainly at the pituitary level.