Site of the in vivo stimulatory effect of prostaglandins on LH release

Lack of effects of indomethacin on estradiol feedback control of luteinizing hormone in ovariectomized ewes

We tested the hypothesis that indomethacin, a potent inhibitor of prostaglandin synthesis, would modify estradiol's effects on tonic and surge concentrations of LH in chronically ovariectomized ewes during the anestrous season. Ewes (n = 21) were assigned randomly to one of four treatments: Vehicle+Blank (n = 5); Indomethacin+Blank (n = 6); Vehicle+Estradiol (n = 5); or Indomethacin+Estradiol (n = 5). On d=0 (hr = 0), ewes began to receive i.m. injections of either indomethacin (4 mg/kg body weight) or corn oil every 8 hr for 9 d. Blood samples were collected every 12 min for 6 hr beginning at -6 hr, +18 hr, and on day 8 (relative to initial injections of indomethacin or vehicle) to assess tonic patterns of secretion of LH. At +24 hr, ewes received blank- or estradiol-containing Silastic implants and were bled hourly for 48 hr. On day 9, ewes received 50 micrograms of GnRH i.v. and were bled hourly for 8 hr. Serum samples were assayed for LH. Indomethacin had no effect on the following parameters of LH secretion: 1) mean concentrations (ng/ml; 8.4 +/- .7 vs 8.9 +/- .8; P > .1), 2) pulse frequency/6 hr (4.5 +/- .4 vs 4.1 +/- .4; P > .1) or 3) pulse amplitude (ng/ml; 15.3 +/- 1.1 vs 14.9 +/- 1.2; P > 1). Estradiol elicited a surge of LH which began 18.9 +/- 1.7 hr after implant insertion, reached a mean peak concentration of 95.3 +/- 20.1 ng/ml, and did not differ with respect to indomethacin treatment (P > .1).(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone-releasing factor (GRF) stimulates PGE2 production in rat anterior pituitary. Evidence for a PGE2 involvement in GRF-induced GH release

Rat anterior pituitaries were incubated over a 3-h period. Both PGE2 and GH were increased by GRF in a concentration-related manner (ED50: 3.5 nM and 6.5 nM, respectively). A significant correlation (r = 0.88, n = 127) was observed between GH and PGE2 release over the range of GRF concentrations tested. Among the five prostanoids analyzed, only PGE2 was selectively increased. Somatostatin lowered GH release, without any effect on PGE2 production. Indomethacin (Id) and Aspirin reduced significantly PGE2 synthesis and GRF-induced GH release. The inhibitory effect of Id was counteracted by addition of PGE2 to the medium. GRF and PGE2, at maximal concentrations, had a partial additive effect on GH release. The increase in PGE2 production and the reduced GH release in the presence of cyclooxygenase inhibitors suggest that PGE2 is involved in GRF-induced GH release.

Prostaglandin E2: a neuromodulator in the central control of gastrointestinal motility and feeding behavior by calcitonin

Two micrograms of prostaglandin E2 injected into the lateral ventricle of the brain in rats had the same anorectic and gastrointestinal motor effect as central administration of 0.02 unit of calcitonin. The effects of calcitonin were blocked by a previous intracerebroventricular administration of 0.25 milligram of indomethacin. These results suggest that both anorectic and gastrointestinal motor effects of calcitonin are centrally mediated by the release of prostaglandins.

Growth hormone-releasing factor stimulates adenylate cyclase activity in the anterior pituitary gland

Synthetic human pancreatic growth hormone-releasing factor (hpGRF)(1-40)-NH2 stimulates adenylate cyclase activity in rat anterior pituitary particulate fraction at an ED50 value of approximately 150 nM. GTP more than doubles the stimulatory effect of hpGRF and PGE2 on [32P] cyclic AMP formation. The present data show that hpGRF as well as PGE2, another potent stimulus of GH secretion, act at least partly, through GTP-dependent mechanisms in their coupling with adenylate cyclase.

LHRH test in Bartter's syndrome before and during treatment with prostaglandin synthesis inhibitors

LHRH tests were performed in two children with Bartter's syndrome before and during treatment with prostaglandin synthesis inhibitors. Before treatment, in patient 1 both basal and peak FSH and LH levels were elevated; in patient 2 basal and peak FSH levels were above the normal range, while basal and peak LH levels were normal. During treatment with an inhibitor of prostaglandin synthesis, abnormal values decreased into the normal range. These results support a possible role of endogenous prostaglandins in regulating gonadotrophin secretion in humans.

Serum luteinizing hormone, testosterone, prolactin and cortisol concentrations after PGF2 alpha in the boar

The effect of prostaglandin F2 alpha (PGF2 alpha) on serum luteinizing hormone (LH), testosterone (T), prolactin (PRL) and cortisol (CS) was studied in the boar. Indwelling cannulae were placed nonsurgically in the jugular vein of six 8 to 9 month-old boars weighing 130 to 160 kilograms. Twenty-four hr after cannulation, blood samples were collected every 30 min from 0630 to 1830 hours. Immediately after the second blood sample (0700 hr) three boars were injected intramuscularly (IM) with 20 mg PGF2 alpha and three boars were injected IM with saline (C). Serum concentrations of LH, T, PRL and CS were quantitated by radioimmunoassay. Serum LH and T concentrations were similar for the PGF2 alpha and C boars throughout the sampling period. In contrast, PRL and CS increased from basal concentrations (mean +/- SE) of 2.1 +/- .1 ng/ml and 24.0 +/- .9 ng/ml to 11.6 +/- .3 ng/ml and 86.9 +/- 9.8 ng/ml, respectively, within 30 min after PGF2 alpha injections and then decreased to control levels over the next 2.0 to 2.5 hours.

Lordosis induction in the rat by prostaglandin E2 systemically or intracranially in the absence of ovarian hormones

Within 20 minutes of an intraperitoneal injection, PGE2 induced lordosis responding to manual stimulation in 6 of 9 rats that were ovariectomized-hysterectomized and hormonally untreated. Similarly, intracranial application of PGE2, through guide cannulae that were chronically-implanted in the basal hypothalamus, induced lordosis responding to manual stimulation within 10 minutes in ovariectomized, hormonally-untreated rats.

Further studies on prostaglandin E2 (PGE2)-induced gonadotropin release: comparison with the effect of 15-methyl PGE2, PGAs, PGBs and prostaglandin endoperoxide analogs

It is known that PGE2 is a potent stimulus of LH release. To determine if the effect of PGE2 could be enhanced and/or prolonged by retarding its metabolic degradation, a derivative, 15-methyl PGE2 (15-E2) which is more slowly degraded than the natural compound was injected intravenously (i.v.) at various dose levels or into the third ventricle (3rd V) of ether-anesthetized, ovariectomized, estrogen (OVX, Eb)-treated rats and its effect on gonadotropin release was compared with that of PGE2. Both PGs injected i.v. were equally effective in increasing plamsa LH and maintaining the elevated levels, although 15-E2 induced a larger and more sustained increase in plasma FSH than PGE2. By contrast, 3rd V PGE2 was clearly more effective than 3rd V 15-E2 in releasing LH and to a lesser extent, FSH. The effect of 15-E2 on LH was similar to that produced by 3rd V PGE1, injected at a similar dose. However, its effect on FSH was greater than that of PGE1. To evaluate the effect(s) of prostaglandins of the A and B series on gonadotropin release, PGA1, PGA2, PGB1 or PGB2 were injected intraventricularly in OVX, Eb-treated rats. PGBs were injected into conscious, free-moving rats. PGA2 or PGB2 increased plasma LH concentrations although much less effectively than PGE2. Third V PGA1 or PGB1 were ineffective. The 3rd V injection of two cyclic esters (U-44069 and U-46619), stable analogs of the PG endoperoxide PGG2 and PGH2, induced a small, transient increase in LH levels and did not alter plasma FSH in conscious, free-moving animals. PGE2 injected intraventricularly at a similar dose was demonstrated to be mcuh more potent than the analogs in stimulating LH and FSH release. The results indicate that: 1) 15-E2, in spite of its described long-lasting activity, does not appear to be more potent than the natural compound in releasing LH, although when injected i.v., it appeared to induce a more sustained increase in plasma FSH; 2) although PGA2 and PGB2 can also act centrally to stimulate LH release, their low potency suggests that this is a pharmacological effect; and 3) the two analogs of PG endoperoxides tested proved to be poor stimuli for gonadotropin release. The significance of these findings is discussed.