Concomitant inhibition of pulsatile luteinizing hormone (LH) and stimulation of prolactin release by prostacyclin (PGI2) in ovariectomized (OVX) conscious rats

Abstract Prostacyclin (PGI 2 ) or its stable metabolite, 6-keto-PGF 1α (1–5 μg) in 2.5 μl 0.05 M phosphate buffer (pH 7.4), was injected into the third vertricle (3 V) of ovariectomized (OVX), freely moving rats. Control animals received 2.5 μl of buffer. In the initial experiments a control blood sample was taken and then the PGI 2 was injected and frequent samples taken thereafter. With this protocol injection of 2 μg of PGI 2 produced a significant decrease in mean plasma LH only at 60 min after its injection (p 2 or 6-keto-PGF 1α . Intraventricular injection of phosphate buffer failed to modify the characteristic pulsatile release of LH and did not alter plasma PRL levels. The amplitude of LH pulses was significantly reduced by PGI 2 and the inhibitory effect was dose-related. Even a dose of 1 μg produced a significant reduction in pulse height and the response was graded with maximal reduction occurring with the 5 μg dose which essentially abolished the LH pulses. Following the microinjection of 6-keto-PGF 1α , no significant changes were observed in plasma LH values and the pulses of the hormone. Five μg PGI 2 considerably elevated plasma PRL values during the 20–25 min following its 3V injection, whereas the same dose of 6-keto-PGF 1α produced only a very slight stimulatory effect. Since PGI 2 had no effect to alter LH release by cultured pituitary cells in vitro , it is concluded that PGI 2 can act on structures near the 3V to inhibit pulsatile release of LHRH.