Modulation of cyclic AMP formation and progesterone secretion by human chorionic gonadotropin, epinephrine, buserelin and prostaglandins in normal or human chorionic gonadotropin desensitized rat immature luteal cells in monolayer culture

Mutations of gonadotropins and gonadotropin receptors: elucidating the physiology and pathophysiology of pituitary-gonadal function

The recent unraveling of structures of genes for the gonadotropin subunits and gonadotropin receptors has provided reproductive endocrinologists with new tools to study normal and pathological functions of the hypothalamic-pituitary-gonadal axis. Rare inactivating mutations that produce distinctive phenotypes of isolated LH or FSH deficiency have been discovered in gonadotropin subunit genes. In addition, there is a common polymorphism in the LHbeta subunit gene with possible clinical significance as a contributing factor to pathologies of LH-dependent gonadal functions. Both activating and inactivating mutations have been detected in the gonadotropin receptor genes, a larger number in the LH receptor gene, but so far only a few in the gene for the FSH receptor. These mutations corroborate and extend our knowledge of clinical consequences of gonadotropin resistance and inappropriate gonadotropin action. The information obtained from human mutations has been complemented by animal models with disrupted or inappropriately activated gonadotropin ligand or receptor genes. These clinical and experimental genetic disease models form a powerful tool for exploring the physiology and pathophysiology of gonadotropin function and provide an excellent example of the power of molecular biological approaches in the study of pathogenesis of diseases.

Effects of prolactin on steroidogenesis and cAMP accumulation in rat luteal cell cultures

The effects of prolactin (PRL), alone and as a modulator of human chorionic gonadotropin (hCG) action, on steroidogenesis and cAMP accumulation in rat luteal cell cultures were examined. Cultured rat luteal cells were prepared from immature rats primed with pregnant mare serum gonadotropin and hCG. In vitro treatment was performed with 0.1 and 0.2 IU/ml hCG and 1-100 ng/ml PRL. Cultures were incubated for 48 h for evaluation of progesterone (P4) secretion and for 1 h for measurement of cAMP accumulation. The same doses of hormones and incubation periods were also used in preovulatory rat granulosa cell cultures and found to cause a significant, dose-dependent inhibition in estradiol, P4 and cAMP accumulation. In luteal cell cultures, on the other hand, P4 secretion was significantly elevated, in a dose-dependent manner, by PRL. Moreover, identical doses of PRL caused a significant, dose-dependent stimulation of cAMP accumulation. Basal levels of P4 were also significantly elevated by PRL alone, but no such stimulation by PRL was detected in basal levels of cAMP. Addition of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, increased the stimulation of P4 and cAMP by hCG + PRL in a manner dependent on PRL concentrations. The overall data therefore demonstrate divergent effects of PRL on cAMP accumulation and steroidogenesis in the ovary: inhibitory in the preovulatory and stimulatory in the postovulatory state. Moreover, these findings suggest a possible common mechanism linking the effects of PRL before and after ovulation: inhibition of cAMP accumulation via enhanced breakdown of the nucleotide.

Insulin regulation of steroidogenic activity in rat culture luteal cells

The effect of insulin on the function of rat luteal cells in monolayer culture was examined. Cells were obtained from PMSG-hCG primed immature rats and further cultured in serum free medium with or without insulin. The hormone produced an increase of progesterone production and maximal stimulation was achieved at 0.2 nM of insulin (100% stimulation). This effect was enhanced by addition of methyl-isobutyl-xantine (MIX 0.1 mM) to the culture medium. However, the stimulation produced by LH was not augmented by the presence of insulin. The conversion of progesterone into 20 alpha-hydroxy-progesterone was also enhanced after insulin treatment. Luteal cells were also cultured in the presence of 25-hydroxy-cholesterol (10 micrograms/ml). In these conditions insulin produced a 2-fold increase in progesterone production. Aromatase activity was assessed by adding androstenedione (0.25 microM) as substrate. Insulin produced a 14-fold stimulation of estradiol production after 24 h of culture. Insulin action was tested in short time incubations of luteal cells in a glucose free medium, in these experiments the hormone was able to induce a significant increase in progesterone and 20 alpha-hydroxy-progesterone production. These data suggest that luteal cell function is regulated by insulin and that this hormone has a direct effect on the steroidogenic process.