Isoproterenol-stimulated hormone

Potentiation of hormone responses In membranes has been more difficult to observe. Forskolln can potentiate prostaglandin stimulation of adenylate cyclase in human platelet membranes nd Isoproterenol stimulation of adenylate cyclase In membranes from wild type S49 lymphoma cells and rat adipocytes.These potentlatlons are not nearly as large as those seen in Intact cells and tissues. 

However, the levels of Gsa, Gia-1, Gia-2, Gia-3, Goa, and Gp were also shown to be unaltered in myocardium from SHRs, and adenylyl cyclase activity stimulated by PGEi, glucagon, and isoproterenol was reduced in SHRs, whereas FSK-stimulated enzyme activity was greater in SHRs as compared to WKY (McLellan et al. 1993). On the other hand, a diminished stimulation of adenylyl cyclase by stimulatory hormones, guanine nucleotides, FSK, and NaF in aorta and heart sarcolemma from SHRs (Anand-Srivastava 1992), renal hypertensive rats (Anand-Srivastava 1988) 1K1C HRs (Ge et al. 1999, 2006), and DOCA-salt HRs (Anand-Srivastava et al. 1993) has been demonstrated The reduction in the hormone receptor binding sites may be one of the possible mechanisms responsible for such an impaired response of hormones (Limas and Limas 1978 Woodcock et al. 

The effect of catecholamines on System A activity has been tested in freshly isolated cells as well. Freychet and his colleagues (50,57) showed that most of the stimulatory action of epinephrine was mediated by a-adrenergic receptors. Phentolamine blocked about 90% of the epinephrine-induced transport, while the )9-antagonist propanolol reduced the hormonal stimulation by only 15% (50). Furthermore, epinephrine was more potent by an order of magnitude than isoproterenol with respect to enhancement of transport (50). 

Isoproterenol (Iso) increased avUCP expression (+67% after I h of stimulation), as previously observed in vivo in chicken muscle, but to a greater extent (9 fold-increase Joubert et al, 2010). This discrepancy could be explained by the concomitant effect of isoproterenol on other factors regulating muscle metabolism in vivo, such as plasma thyroid hormones or blood metabolites that could not be investigated here. The use of fatty acid supplement (FA) induced a delayed increase in avUCP expression (+54% after 2 h of stimulation) and was associated with stronger activations of p38 MAPK and AMPK than with isoproterenol. 

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