Influence of adrenodemedullation on beta 2- and beta 3-adrenoceptors mediating relaxation of oesophageal smooth muscle of spontaneously hypertensive rats

Estrogen regulates adrenal medullary function producing sexual dimorphism in nociceptive threshold and beta-adrenergic receptor-mediated hyperalgesia in the rat

Epinephrine produces sexually dimorphic beta(2)-adrenergic receptor-mediated mechanical hyperalgesia, with male rats exhibiting greater hyperalgesia. Because female rats have higher plasma epinephrine levels, and beta-adrenergic receptor sensitivity is affected by chronic exposure to agonists, we tested the hypothesis that this sexual dimorphism is due to epinephrine-induced desensitization of beta(2)-adrenergic receptors. Following gonadectomy, epinephrine hyperalgesia, as measured by the Randall-Selitto paw-withdrawal test, was unchanged in male rats while in females it was increased. Prepubertal male and female rats do not demonstrate sexual dimorphism in either plasma epinephrine level or epinephrine-induced hyperalgesia. Adrenal medullectomy and adrenal denervation both significantly enhanced epinephrine hyperalgesia, but only in females. In contrast, the sexually dimorphic hyperalgesia induced by prostaglandin E(2), another agent that acts directly to sensitize primary afferent nociceptors, was not enhanced by adrenal medullectomy or denervation. Chronic administration of epinephrine in male rats, to produce plasma levels similar to those of gonad-intact females, significantly attenuated epinephrine-induced hyperalgesia, making it similar to that in females. These results strongly support the suggestion that estrogen regulates plasma epinephrine in female rats and differential sensitivity to beta(2)-adrenergic agonists accounts for the sexual dimorphism in epinephrine-induced hyperalgesia. Unexpectedly, regulation of adrenal medullary function by estrogen was also found to modulate baseline nociceptive threshold such that females had a lower nociceptive threshold.

Modulation of beta2- and beta3-adrenoceptor-mediated relaxation of rat oesophagus smooth muscle by protein kinase C

Although a prominent role for protein kinase C (PKC) in the cross-talk between the phosphoinositide pathway and beta2-adrenoceptor signalling has been indicated, modulation of beta3-adrenoceptor function by PKC has not been studied thus far. In the present study, we have compared the relative capacity of PKC in modulating beta2- and beta3-adrenoceptor-mediated relaxation of methacholine-contracted rat oesophagus smooth muscle. To this purpose the effects of the PKC-inhibitor GF 109203X (2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimide) on relaxation induced by fenoterol, formoterol, (-)-noradrenaline, BRL 35135 (4-[2-[(2-hydroxy-2-(chlorophenyl)ethyl)amino]-propyl]-phenoxyacetic-acidmethylester) and IBMX (3-isobutyl-1-methyl-xanthine) were studied, in the absence and presence of the selective beta2-adrenoceptor antagonist ICI 118,551 (erythro-1(7-methylindan-4-yloxy)-3-(isopropylamin)-butan-2-ol). Our results show that inhibition of PKC resulted in differential augmentation of both beta2- and beta3-adrenoceptor-mediated relaxation. In contrast, relaxation induced by IBMX was not influenced at all by GF 109203X. The beta2-adrenoceptor bears phosphorylation sites for several kinases, including PKC. Since the beta3-adrenoceptor lacks these consensus sites, the results may also indicate that PKC-mediated Galphas phosphorylation is involved in the cross-talk between the muscarinic receptor-mediated phosphoinositide pathway and beta2- and, particularly, beta3-adrenoceptor signalling.