Protein kinase A and/or C inhibitors potentiate isoproterenol-induced cyclic AMP accumulation in intact human lymphocytes

Clomiphene citrate inhibits gonadotropin-induced ovulation by reducing cyclic adenosine 3',5'-cyclic monophosphate and prostaglandin E2 levels in rat ovary

OBJECTIVE

To determine whether clomiphene citrate (CC) inhibited gonadotropin-induced ovulation by reducing cyclic adenosine 3',5'-cyclic monophosphate (cAMP) and prostaglandin E2 (PGE2) levels in ovary. If so, to determine whether E2 coadministration could protect against these effects of CC.

DESIGN

A controlled prospective study.

SETTING

Laboratory research setting in the department of reproductive biomedicine at a national research institute in India.

ANIMAL(S)

Sixty sexually immature female rats that were 24-25 days of age.

INTERVENTION(S)

The sexually immature female rats were given a single injection (10 IU i.m.) of pregnant mare serum gonadotropin. After 48 hours, the rats were given single injections of hCG (10 IU) along with CC, with or without E2, for 16 hours.

MAIN OUTCOME MEASURE(S)

Number of superovulated COCs, ovary and uterus weight, FSH and LH levels in serum, and cAMP and PGE2 levels in ovary.

RESULT(S)

The superovulatory dose of gonadotropins significantly increased ovary and uterus weights, cAMP and PGE2 levels in ovary, and serum levels of FSH and LH. Coadministration of CC (10 mg/kg body weight) significantly reduced levels of cAMP, PGE2 in the ovary, ovary and uterus weights, and ovulation rate, whereas FSH and LH levels were not significantly altered. Supplementation of E2 protected against these inhibitory effects of CC and augmented levels of FSH and LH in serum.

CONCLUSION(S)

Clomiphene citrate inhibited gonadotropin-induced ovulation by reducing cAMP and PGE2 levels in the ovary, and E2 protected against these effects of CC on gonadotropin-induced ovulation in rat.

Enhancement of beta-adrenergic-induced cAMP accumulation in activated T-cells

Agonist stimulation of the beta-adrenergic receptor on T-cells results in the production of cAMP, which has been correlated with modulation of T-cell function. In previous studies, we have demonstrated that the mitogen PHA can synergistically enhance the accumulation of cAMP in T-cells in response to the agonist isoproterenol. In this report we have investigated the mechanisms by which dual stimulation of T-cells acts to synergistically enhance cAMP accumulation. The results demonstrate that increasing the levels of intracellular calcium with ionomycin or thapsigargin enhanced isoproterenol-induced cAMP accumulation in T-cells. In contrast, PHA enhanced isoproterenol-induced cAMP by a calcium-independent mechanism as evidenced by stimulation with isoproterenol plus PHA in calcium-free medium. Further studies revealed that PHA prevented both sequestration of the beta-adrenergic receptor and its dissociation from Gs protein in response to isoproterenol stimulation. In contrast, PHA did not prevent the functional uncoupling of the beta-adrenergic receptor from adenylyl cyclase, suggesting that additional mechanisms are likely involved. In summary, these studies demonstrate that dual receptor signalling of T-cells increases cAMP accumulation and offers a potential mechanism for catecholamine modulation of T-cell function.

Roles of second-messenger systems and neuronal activity in the regulation of lordosis by neurotransmitters, neuropeptides, and estrogen: a review

Many neurotransmitters and neuropeptides can affect the rodent feminine sexual behavior, lordosis, when administered in the ventromedial hypothalamus (VMH), midbrain central gray (MCG), or other brain regions. A survey of the electrophysiological and biochemical actions of these neural agents revealed that there is a very consistent association between lordosis facilitation with both the activation of the phosphoinositide (PI) pathway and the excitation of VMH and MCG neurons. In contrast, lordosis inhibition is associated, less consistently, with alterations of the adenylate cyclase (AC) system and the inhibition of neuronal activity. The findings that lordosis could be facilitated by going beyond membrane receptors and directly activating the PI pathway, suggest that this second-messenger pathway is a common mediator for the lordosis-facilitating agents. Furthermore, as in the case of stimulating membrane receptors, direct activation of this common mediator also requires estrogen priming for lordosis facilitation. Therefore, it is likely that the PI pathway is modulated by estrogen in the permissive action of estrogen priming. Indeed, a literature review shows that estrogen can affect selective isozymes of key enzyme families of the PI pathway at various levels. Such selective modulations, at several levels, could easily alter the course of a PI cascade; thence, the eventual functional outcome. These findings prompt us to propose that estrogen enables lordosis to be facilitated by a selective modulation of the PI pathway.