Investigation of cardiac beta-adrenoceptors using 125I-labelled 1-(4-iodophenoxy)-3-isopropylaminopropan-2-ol

Radioiododestannylation: preparation and evaluation of radioiodinated thienyl alcohols

Radioiododestannylations was employed to prepare a series of four specifically labeled thienyl alcohols: 1-(5-iodo-2-thienyl)-cyclopentan-1-ol and -cyclohexan-1-ol; 17 alpha-(5-iodo-2-thienyl)-17 beta-estradiol and -estradiol-3-O-methyl ether. The method utilized 5-(trimethylstannyl)thienyl intermediates which had been prepared in good yields from 2,5-bis(trimethylstannyl)thiophene and the appropriate cyclic ketones. The trimethylstannyl substrates reacted with no-carrier-added Na125I in the presence of 30% H2O2-acetic acid (2:1) at pH 4.5 at ambient temperature for 5-15 min to give, after HPLC separation, the desired 5-[125I]iodothien-2-yl products in greater than 90% isolated yields. Although tissue distribution studies in rats were uneventful, the methodology employed to give the labeled products possesses distinct advantages compared to alternative methods for preparing radioiodinated aryl moieties.

Cardiac beta adrenoceptors and adenylate cyclase in normotensive and renal hypertensive rabbits during changes in autonomic activity

The effects of hypertrophy and alterations in cardiac autonomic activity on left ventricular (LV) beta adrenoceptors and adenylate cyclase were measured in rabbits. Normotensive and renal hypertensive animals were exposed to three levels of chronic sympathetic activity: (i) "normal" activity; (ii) reduced activity after 2 weeks treatment with guanethidine; (iii) 2 weeks increased sympathetic activity following sino-aortic denervation. In hypertensive animals with "normal" activity LV beta receptor sarcolemma concentration was reduced by 36+ compared with the normotensive subgroup whilst total LV receptor numbers were unaltered. Isoprenaline activated adenylate cyclase was similarly affected whilst other sarcolemma marker enzymes were unaffected. Chronic guanethidine administration to normotensive rabbits increased beta receptor concentration (16%, P less than 0.05), basal and isoprenaline activated meters were unaffected. Sino-aortic denervation did not significantly affect beta receptor concentration in either group. The small changes in beta receptor concentration during alterations in sympathetic activity suggest that only a small proportion of LV beta receptors appear to be innervated. The reduction in sarcolemma beta receptor concentration in hypertensive animals appears to be a specific effect due to hypertrophy of the cardiocyte.

Decreased cardiac beta-adrenergic receptors in deoxycorticosterone-salt and renal hypertensive rats

The development of experimental deoxycorticosterone-salt (DOCA-salt) and renal artery clip hypertension in rats is associated with alterations in the sensitivity of the myocardium to adrenergic stimulation. We studied beta-adrenergic receptors and isoproterenol-stimulated adenylate cyclase in myocardial membranes from hypertensive rats to determine whether this altered sensitivity is associated with any change in beta-adrenergic receptors. The specific binding of the beta-adrenergic antagonist, 125I-iodohydroxybenzylpindolol, was used to measure numbers and affinities of receptors in myocardial membrane preparations. Cardiac membranes from both DOCA-salt and renal hypertensive rats showed significantly fewer beta-receptors than did membranes from control, normotensive rats. Receptor affinity remained unchanged. This decrease was from 110 +/- 19 to 49 +/- 5 fmol/mg protein for DOCA-salt hypertension and from 110 +/- 18 to 75 +/- 16 fmol/mg protein for renal artery clip hypertension. Isoproterenol-stimulated adenylate cyclase activity also was lower in membranes from hypertensive rats, whereas basal and fluoride-stimulated activities were unchanged.

Decreased cardiac beta-adrenoceptors in hypertensive rats

1. beta-Adrenoceptors have been investigated in cardiac and renal cell membranes from hypertensive and normal rats. 2. The 125I-labelled beta-adrenoceptor antagonist 1-(4-iodophenoxy)-3-isopropylaminopropan-2-ol was used to measure directly the number and affinity of receptors. 3. Cardiac membranes from hypertensive rats had a lower concentration of beta-adrenoceptors than membranes from control normotensive animals, but the affinities of the receptors remained unchanged. Receptor concentration decreased by half and was similar in each of the three models of experimental hypertension investigated. 4. In contrast, kidney membranes from hypertensive animals had the same beta-adrenoceptor concentration and affinity as membranes from normotensive rats. 5. The decrease in cardiac beta-adrenoceptor concentration may reflect an increase in cardiac sympathetic drive in these experimental hypertensive models.