Differential effect of arachidonic acid on the vasoactive intestinal peptide receptor/effector system in rat prostatic epithelium during sexual maturation

Effects of Pygeum africanum extract (Tadenan) on vasoactive intestinal peptide receptors, G proteins, and adenylyl cyclase in rat ventral prostate

BACKGROUND

Tadenan (a Pygeum africanum extract) is a drug used in the treatment of benign prostatic hyperplasia. Its effects on prostate fibroblast proliferation and bladder function after partial outlet obstruction have been demonstrated in various pharmacological studies. However, its effects at the molecular level are poorly documented.

METHODS

Tadenan was dissolved in peanut oil. Rats were orally given two daily doses of the drug (1 or 10 mg/kg b.w.) for 4 days. Vasoactive intestinal peptide (VIP) binding, adenylyl cyclase stimulation, and expression of G-protein subunits were studied in rat prostatic membranes by established procedures.

RESULTS

Tadenan treatment of castrated/testosterone-replaced rats was performed in order to interfere with prostatic cell proliferation. This experimental approach resulted in increases of: 1) VIP effect on adenylyl cyclase stimulation through alpha(s) G-subunit; 2) alpha(i) activation by low Gpp[NH]p doses (in the presence of forskolin); and 3) alpha(s), alpha(i1/2), and alpha(i3/0) levels. However, there were no modifications in membranes from quiescent, nonproliferating prostates (untreated rats).

CONCLUSIONS

The observed regulatory role of Tadenan on various prostatic components of the adenylyl cyclase system, together with previous findings on protein kinase C-mediated signal transduction, open a complex array of possibilities of direct actions of this phytotherapeutic agent in the prostate.

Effect of flutamide-induced androgen-receptor blockade on adenylate cyclase activation through G-protein coupled receptors in rat prostate

The effect of the antiandrogen flutamide on the prostatic vasoactive intestinal peptide (VIP) receptor/effector system was studied in rats. Rats were s.c. injected with a daily dose of flutamide (15 mg/kg B.W.) or vehicle for 14 days. Drug treatment resulted in histological evidence of gland involution and increased plasma membrane fluidity as estimated by fluorescence spectroscopy. The number of VIP receptors and the stimulatory effect of VIP on adenylate cyclase activity in prostatic membranes decreased in flutamide-treated rats. However, the pattern of forskolin stimulation of the enzyme activity was not modified by this drug. Androgen-receptor blockade by flutamide also decreased the prostatic levels of alpha(s,) alpha(i1/2), and alpha(i3/0) G-protein subunits, as estimated by an immunological procedure. Whereas apoptotic DNA fragmentation was evidenced in prostate from 3-day castrated animals, a heterogeneous electrophoretic pattern was observed after flutamide treatment. Thus, androgen-receptor blockade by flutamide results in an important impairment of the components of the VIP receptor/effector system in rat prostate as well as in a modification of their coupling extent, which is presumably due to differences observed in plasma membrane fluidity. These results represent a crosstalk in the prostate between two mechanisms of signal transduction involved in cell proliferation.

Fatty acids and brain peptides

The role of fatty acids (FA) as a mediator and modulator of central nervous system activity in general, and peptides in particular, is only recently becoming understood. This paper reviews numerous findings concerned with the activity of fatty acids, particularly with their interaction with diverse neurochemical systems and their consequences for better understanding neurotransmitters, hormones and peptides. The effects include FA as precursors in the manufacture of neurochemical elements, including enzymes, neurotransmitters, and hormones. Of particular interest is the important changes in neuronal membrane composition that have been attributed to FA. Such changes may account for the changes in thermoregulation, learning, and other functions that accompany dietary manipulation of FA intake. While the total level of FA has been the object of many investigations, this report addresses the need to focus on the ratio of FA, especially alpha-linolenic/linoleic acid, which has been shown to be a critical factor in a number of research studies.

G-proteins and beta-adrenergic stimulation of adenylate cyclase activity in the diabetic rat prostate

BACKGROUND

The consequences of experimental diabetes on membrane lipids, beta-adrenergic stimulation of adenylate cyclase activity, and G-protein levels in the prostate gland are not defined.

METHODS

Prostatic membranes from control and streptozotocin (STZ)-diabetic rats were used to study adenylate cyclase stimulation as well as for immunodetection of stimulatory (alpha s) and inhibitory (alpha i) G-protein subunits. Changes in membrane lipid composition were estimated by [1-14C] acetate incorporation into lipid subclasses.

RESULTS

The efficacy of isoproterenol on stimulation of adenylate cyclase activity and the levels of alpha s, alpha i1/2, and alpha i3/0 G-protein subunits were drastically reduced in prostatic membranes from STZ-diabetic rats. Insulin treatment of diabetic rats tended to normalize G-protein levels, but it was ineffective on the poor adenylate cyclase response to isoproterenol or forskolin. However, it prevented enzyme desensitization to vasoactive intestinal peptide. The pattern of [1-14C] acetate incorporation into lipid subclasses did not vary with diabetes or insulin treatment.

CONCLUSIONS

STZ-induced diabetes results in desensitization for the beta-adrenergic response of adenylate cyclase, as supported by previous data on the low density of beta-adrenergic receptors and the present results on the general decrease of Gs and Gi proteins levels and even of the enzyme itself in the diabetic rat prostate.