Release of cyclic AMP from macrophages by stimulation with prostaglandins.

The effect of various prostaglandins (PG)on the generation of cyclic AMP in rat peritoneal macrophages has been studied in vitro. PGE1 produced a rapid intracellular accumulation of cyclic AMP which was followed by its release into the extracellular space. More cyclic AMP was released with prostaglandins of the E-type than with A- and F-types. It is suggested that release of cyclic AMP from macrophages may participate in the modulation of leukocyte function.     

Interrelationships between prostaglandins, cyclic AMP and steroids in ovulation.

Ovulation is a complex phenomenon, involving a series of biochemical events within the ovary, leading to the rupture of the follicle. This paper summarizes recent studies in our laboratory of some of these biochemical changes using the rabbit as an experimental model. It has been shown in our laboratory that isolated Graafian follicles obtained from oestrous rabbits synthesize steroids and cyclic AMP when incubated in vitro. Luteinizing hormone added to the incubation medium increased steroidogenesis and cyclic AMP synthesis many fold. When follicles were isolated from rabbits at different times following the ovulatory stimulus (mating or HCG injection) it was found that the in vitro response to LH in terms of steroidogenesis and cylcic AMP synthesis was lost as ovulation approached. In contrast, when prostaglandins (PGF and PGE) were measured in rabbit Graafian follicles it was found that the PGF and PGE levels increased as ovulation approached. From these data and from reports in the literature, we have developed a hypothetical model for ovulation in the rabbit which may help in a better understanding of the ovulatory process.     

Effect of dihydrotestosterone on the growth and function of ovarian follicles in intact immature female rats primed with PMSG

Intact, immature female rats were primed with PMSG and treated with 4 injections of DHT. DHT given at 0, 12, 24 and 36 h caused a significant decrease in the ovulation rate 72 h after the PMSG treatment. Concurrent treatment with oestrogen reversed the inhibitory effects of the androgen. The androgen effect was apparently exerted directly on the ovary since DHT did not alter the surge of LH and FSH which occurred at 58 h after PMSG treatment. The DHT inhibition of ovulation was observed in the treatment cycle as well as in subsequent cycles which followed a second PMSG injection. This finding suggests that intermediate size follicles were also adversely affected by the androgen. To confirm that androgen affects follicles of all size ranges, follicles less than 200 microns, 200-400 microns and greater than 400 microns in diameter were isolated from the ovaries of rats treated with PMSG and DHT or the vehicle. The follicles were isolated by density gradient separation of follicles followed by filtration with pre-calibrated Teflon sieves. In some experiments, granulosa cells were also harvested from isolated follicles. DHT treatment did not affect the numbers of follicles of any size but did reduce the oestrogen content of follicles of all sizes. Follicles from DHT-treated animals contained fewer granulosa cells and the cells from treated animals had lower aromatase activity than did cells from control rats. Taken together, these findings suggest that DHT reduces the ovulation rate by decreasing the number of granulosa cells/follicle and by altering the oestrogen synthetic abilities of the cells. All follicles, regardless of size, were sensitive to androgen treatment.     

Messenger RNA synthesis in the testis of immature rats: effect of gonadotropins and cyclic AMP.

Two hours after the intratesticular injection of FSH, hCG or cyclic AMP, the incorporation of labeled uridine into poly(A)-rich RNA was increased. Pretreatment with actinomycin D inhibited the incorporation of uridine into mRNA. After the seminiferous tubules and interstitial cells were separated by treatment with collagenase, FSH treatment increased mRNA synthesis only in the tubules whereas hCG stimulated mRNA synthesis only in the interstitial cells. Cyclic AMP increased the synthesis of mRNA in both interstitial cells and seminiferous tubules. These results suggest a differential action of the two gonadotropic hormones in the cells of the testis; both effects appear to be mediated by cyclic AMP.     

Malaria enhances cyclic AMP production by immature erythrocytes in vitro.

Infection with a chloroquine-susceptible line of $\text{Plasmodium}$$\text{berghei}$ NYU-2 enhanced the production of cyclic AMP in response to isoproterenol only in immature mouse erythrocytes, which possess a functional hormone-receptor-adenylate cyclase complex. With 10^?7 M isoproterenol the increases in cyclic AMP concentrations (picomoles per 10⁸ erythrocytes) were 19 for a preparation of mature erythrocytes, 81 for a preparation enriched with immature erythrocytes, 25 for a preparation of infected mature erythrocytes, and 900 for a preparation enriched with infected immature erythrocytes. Beta-adrenergic receptor blockade with propranolol prevented this response to isoproterenol but had no effect on the stimulation produced by prostaglandin E₁. These findings indicate that the malaria parasite enhances the responsiveness of a fundamental regulatory system that is intrinsic to immature erythrocytes.     

Hypothalamic cyclic AMP after the injection of ovarian steroids into ovariectomized rats

The effect of ovarian steroids on the concentration of adenosine 3',5'-cyclic monophosphate (cAMP) in the hypothalamus was studied in ovariectomized rats. Ovariectomized rats exhibited a lower cAMP concentration than intact rats. The administration of a single dose of estradiol benzoate (50 micrograms/kg body weight) resulted 3 days later in a rise of cAMP values, but levels did not reach those observed in estrous rats. Progesterone (2 mg/rat) injected 3 days after the priming dose of estradiol benzoate produced 4 h later no further changes in hypothalamic cAMP. The changes in hypothalamic cAMP concentration induced by estrogen treatment depend, at least in part, on noradrenergic inputs, since they were prevented by the injection of the norepinephrine synthesis inhibitor, diethyldithiocarbamate. In addition, administration of the beta-blocking agent, propranolol, to estradiol- and estradiol-progesterone-treated rats lowered the concentration of cAMP in the hypothalamus in a dose-dependent manner. In contrast, the administration of an alpha-blocking agent, phenoxybenzamine, had no effect at the tested concentration. The results of this study indicate that estrogen increases cAMP concentration in the hypothalamus by a noradrenergic mechanism involving beta-receptors. Moreover, the findings suggest that estrogen induces an increase in the number of beta-receptor sites, whereas progesterone increases the apparent propranolol sensitivity for these receptor sites.     

Interactions between parathyroid hormone and prostaglandins on renal cortical cyclic AMP

Effects of parathyroid hormone (PTH) and several prostaglandins (PGs) on cyclic AMP (cAMP) metabolism were studied and compared in isolated renal cortical tubules from male hamsters. Both production and intracellular degradation of cAMP were increased by PTH and each of the PGs tested (PGE2, PGE1, PGI2). Production of cAMP was increased to similar levels by maximal concentrations of PTH and each PG, however, degradation of cAMP was significantly higher in response to PTH than with any of the PGs. This difference in intracellular degradation of cAMP was responsible for the much higher concentrations of cAMP in renal cortical tubules exposed to PGs (PGE1, PGE2, PGI2) than to PTH. Submaximal amounts of each PG produced additive increases in cAMP concentrations in the presence of maximal amounts of PTH. Additivity of the combined responses was lost, however, as the PGs concentrations reached their maxima. The results suggest that renal PGs (PGE2 and PGI2) may modulate the effects of PTH on cAMP concentrations in renal cortical tubules.     

Superovulation in beef cattle with PMSG and prostaglandins or progestins

The ovarian response to 2000 I.U. PMSG of 76 suckler cows and 153 heifers synchronized by either progesterone (Abbovestrol-PRID/ CEVA), a synthetic gestagen (Norgestomet/ Intervet), prostaglandin F₂ (Dinolytic/ Upjohn) or a prostaglandin analog (Estrumate/ ICI) was recorded after slaughter. The proportion of animals responding with at least one ovulation was between 82 and 92% except for heifers treated with estrumate (56%). Heifers had nearly twice as many ovulations as cows (11.9 ± 0.9 vs 6.8 ± 0.8 (SEM)). The response was slightly more consistent in gestagen-synchronized animals: nevertheless, individual variation was considerable.     

Interactions between parathyroid hormone and prostaglandins on renal cortical cyclic AMP

Effects of parathyroid hormone (PTH) and several prostaglandins (PGs) on cyclic AMP (cAMP) metabolism were studied and compared in isolated renal cortical tubules from male hamsters. Both production and intracellular degradation of cAMP were increased by PTH and each of the PGs tested (PGE₂, PGE₁, PGI₂). Production of cAMP was increased to similar levels by maximal concentrations of PTH and each PG, however, degradation of cAMP was significantly higher in response to PTH than with any of the PGs. This difference in intracellular degradation of cAMP was responsible for the much higher concentrations of cAMP in renal cortical tubules exposed to PGs (PGE₁, PGE₂, PGI₂) than to PTH. Submaximal amounts of each PG produced additive increases in cAMP concentrations in the presence of maximal amounts of PTH. Additivity of the combined responses was lost, however, as the PGs concentrations reached their maximas. The results suggest that renal PGs (PGE₂ and PGI₂) may modulate the effects of PTH on cAMP concentrations in renal cortical tubules.     

Guinea pig anaphylaxis: time course of changes in cyclic AMP and cyclic GMP.

The time course of changes in the levels of cyclic AMP and GMP and in histamine and prostaglandin release following the onset of anaphylaxis in guinea pig lung (sliced, minced and whole perfused) was studied. A parallel change in the cyclic nucleotide levels was found. There was an initial increase, followed by a decrease, and a subsequent greater and more prolonged increase. Significant histamine and prostaglandin release occurs at approximately the same time while prostaglandin metabolite is released later. Metiamide does not affect histamine or prostaglandin release but abolishes the initial cyclic nucleotide peak and delays the appearance of the secondary increase. The pattern of cyclic nucleotide changes in lung tissue thus appears to be different from that in isolated mast cells. The initial and late increases might be the response of two different cell populations to histamine.