Effect of estrogen on muscarinic acetylcholine receptor expression in rat myometrium.

We report the effect of acute estrogen treatment in the expression of muscarinic acetylcholine receptors (mAChRs) in myometrium. Strips were obtained from rats in estrus (control) and treated with estrogen, 24h before the experiments. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed and m2, m3 and m5 mAChR mRNA subtypes were detected in myometrium from both groups. [(3)H]Quinuclidinyl benzilate [(3)HQNB] binding studies indicated that estrogen treatment did not change the affinity and density of mAChRs in myometrial membranes. Displacement curves of [(3)HQNB] with different mAChRs antagonists indicated a one-site fit for all antagonists tested. Comparison of pK(i) values indicated a significant correlation to M(2)-mAChR subtype. Functional studies, however, showed that estrogen treatment increased myometrium sensitivity to carbachol and the calculated apparent affinity values were significantly correlated to M(3)-mAChR. Furthermore, the pharmacological profile of the two populations of mAChR was not affected by estrogen. In conclusion, these results provide evidence for the presence of M(2)- and M(3)-mAChR, at the mRNA and protein level, in the rat myometrium and indicate that estrogen induces an increase in myometrial responsiveness to mAChR agonists.

Angiotensin receptor in the heart of Bothrops jararaca snake

Angiotensin II interacts with specific cell surface angiotensin AT1 and AT2 receptors and, in some vertebrates, with an atypicalangiotensin AT receptor. This study was designed to characterize the angiotensin receptor in the heart of Bothrops jararaca snake. Aspecific and saturable angiotensin II binding site was detected in cardiac membranes and yielded Kds7.34"1.41 nM and Bmaxs72.49"18 fmolrmg protein. Competition-binding studies showed an angiotensin receptor with low affinity to both angiotensin receptorantagonists, losartan Ž2-n-butyl-4-chloro-5-hydroxymethyl-1-wŽ2X-Ž1H-tetrazol-5-yl.biphenyl-4-yl.methylximidazole. and PD123319 ŽŽ s.-1-Ž4-wdimethylaminox-3-methylphenyl.methyl-5-Ždiphenylacetyl.-4,5,6,7-tetrahydro-1H-imidazow4,5-cxpyridine-6-carboxylate.. Studies onthe intracellular signaling pathways showed that phospholipase Crinositol phosphate breakdown and adenylylcyclasercyclic AMPgeneration were not coupled with this angiotensin receptor. An adenylylcyclase enzyme sensitive to forskolin was detected. The resultsindicate the presence of an angiotensin receptor in the heart of B. jararaca snake pharmacologically distinct from angiotensin AT1 andAT2 receptors. It seems to belong to a new class of angiotensin receptors, like some other atypical angiotensin AT receptors that havealready been described.

A systematic fractionation of crotalus durissus terrificus venom

1. O veneno de C. d. terrificus foi fracionado de forma a obter da mesma preparaçäo: 5'-nucleotidase, fosfodiesterase, enzima tipo trombínico, fosfolipase A2, crotapotina, convulxina e giroxina. Todas estas proteínas foram purificadas até a homogeneidade a eletroforese em acrilamina na presença de dodecil-sulfato de sódio. 2. Em outras fraçöes foram identificadas a presença de L-amino oxidase, atividade de kalikreina tipo tissular e NAD-hidrolase. 3. Uma das fraçöes homogeneas apresentou uma atividade tóxica produzindo sintomas diferentes dos das toxinas conhecidas. Tem uma peso molecular de 8.600 Daltons. 4. A atividade da fosfolipase A2 do veneno e das fraçöes foi completamente inibida pela crotapotina, e esta inibiçäo é específica para a fosfolipase do veneno do Crotalus, e nao ocorre com a atividade de fosfolipase A2 do veneno da Bothrops jararaca, Bothrops moojeni e Tityus bahiensis