Hormone Receptor Sites Research Articles

Pharmacology of the Malpighian tubules of Rhodnius and Carausius: the structure-activity relationship of tryptamine analogues and the role of cyclic AMP.

ABSTRACT 5-Hydroxytryptamine (5-HT) and a few of its derivatives will cause an acceleration of secretion by the isolated Malpighian tubules of Rhodnius prolixus and Carausius morosus. Substitution in the terminal amino group of 5-HT causes little loss of effect, but changes in the indole ring and the hydroxy group in general abolish activity. Most derivatives of 5-HT which do not stimulate secretion, and many other related amines, act as inhibitors of secretion in Rhodnius. This inhibition is probably of the competitive type. Substances which stimulate secretion in Rhodnius are easily washed off the Malpighian tubules, although they will stimulate secretion at very low concentrations By contrast, competitive inhibitors wash away relatively slowly and inhibit only at much higher concentrations. It is suggested therefore that stimulation involves only momentary interactions between stimulant and receptor sites, but that competitive inhibitors spend considerably longer attached to the sites. Cyclic 3 ′,5 ′ -adenosine monophosphate (cyclic AMP) will stimulate secretion by tubules of both Rhodnius and Carausius. Tubules of both species are very sensitive to cyclic AMP, measurable effects being produced at concentrations of 4×10−5 M/ l in Rhodnius and 10−4 M/ l in Carausius. Aminophylline (theophylline ethylene diamine) at a concentration of 10−4 M/ l stimulates secretion by Carausius tubules. This compound and other inhibitors of phosphodiesterase have no stimulatory action on Rhodnius tubules, but any such effect may be masked by the adverse reaction of the tubules to the high concentrations necessary. Inhibitors of 5-HT action such as tryptamine and tyramine also inhibit secretion by Rhodnius Malpighian tubules induced by cyclic AMP. This may be due to a dependence of the action of cyclic AMP on the state of the diuretic hormone receptor site. The evidence is consistent with the idea that 5-HT, other stimulant molecules related to 5-HT and the diuretic hormones interact with Malpighian tubule cells of Rhodnius and Carausius at specific sites, probably on the cell membrane facing the haemolymph. As a result of this, secretion is induced, possibly through the action of intracellular cyclic AMP produced as a response.

Independence of the Effects of Epinephrine, Glucagon, and Adrenocorticotropin on Glucose Utilization from Those on Lipolysis in Isolated Rat Adipose Cells

Abstract The stimulatory effects of epinephrine, glucagon, and adrenocorticotropin (ACTH) upon lipolysis and on the uptake and oxidation of glucose were studied in isolated rat epididymal adipocytes. Under conditions in which prostaglandin E1 (PGE1) and nicotinic acid were antilipolytic against epinephrine, these agents were without influence on the effects of the hormone on the metabolism of glucose. Furthermore, the synergistic effects of caffeine and theophylline on epinephrine-induced lipolysis were not seen in studies of epinephrine-stimulated glucose oxidation. Since epinephrine increased the uptake and oxidation of glucose under conditions which either did (presence of bovine serum albumin) or did not (absence of bovine serum albumin) permit accumulation of free fatty acids, it is unlikely that free fatty acids mediate the effects of epinephrine on glucose entry and oxidation in adipocytes. Since two β-adrenergic blocking agents, Ko 592 and propranolol, inhibited epinephrine's stimulation of both lipolysis and glucose oxidation, it appears that both effects of the hormone involve β-receptors. While PGE1, Ko 592, and propranolol all inhibited the stimulatory effects of glucagon and ACTH on lipolysis in adipocytes, neither agent influenced the action of either hormone on glucose oxidation; the latter finding suggests that β-receptors do not mediate the stimulatory effects of these hormones on glucose oxidation. Ko 592 and propranolol were several orders of magnitude more potent as antilipolytic agents against epinephrine than they were against ACTH and glucagon. Excessive amounts of PGE1 only partially inhibited the lipolytic effect of even submaximal concentrations of epinephrine, glucagon, and ACTH in adipocytes, although total inhibitions were obtainable with appropriate concentrations of the β-adrenergic blocking compounds. Such observations suggest that the adenyl cyclase system for the synthesis of adenosine 3',5'-cyclic monophosphate in adipocytes contains at least two different types of activation receptor sites for hormones, and that PGE1 binds to only one type of site while the β-adrenergic blockers are effective against both types. The present, and previous, data permit the conclusion that epinephrine, ACTH, and glucagon stimulate the entry and over-all oxidation of glucose in adipocytes by a mechanism which is distinct from that (or those) by which these hormones promote lipolysis.

Agents for alkylating steroid hormone receptors. I. Analogs derived from esters of 17 α-hydroxyprogesterone

A method designed to selectively tag hormonal receptor sites is discussed. Acylation of 17 α-hydroxyprogesterone with the half acids, half esters of glutaric, adipic, and pimelic acids followed by selective hydrolyses afforded the ω-carboxybutanoate, the ω-carboxypentanoate, and the ω-carboxyhexanoate of 17 α-hydroxyprogesterone. These acids were converted via their acid chlorides to the 5-keto-6-diazohexanoate, the 6-keto-7-diazoheptanoate, and the 7-keto-8-diazooctanoate of 17 α-hydroxyprogesterone. The latter compounds were active in the Clauberg assay, but they appear not to have alkylated the Clauberg receptor.

Distribution of enzyme systems responsible for steroid metabolism in different tissues and subcellular fractions.

FROM their studies of the in vivo metabolism of various biologically active and inactive 11-oxygenated steroids, Bush and Mahesh1 believe that the glucocorticoid activity of these steroids is due to the specific interaction of an llβ-hydroxy group on the steroid molecule with the receptor sites for such hormones, and that such an interaction does not involve oxidation-reduction at C–11. However, Talalay and co-workers2 observed that various hydroxy-steroids, including the 11-oxygenated ones, can act as coenzymes in the transfer of hydrogen between pyridine nucleotides in the presence of suitable steroid dehydrogenases and they suggest that this is the mode of action of steroid hormones. In the present study, the metabolism of cortisol and cortisone has been investigated in various tissues in order to determine the distribution of enzyme systems responsible for the metabolism of the steroids, with the view of finding out whether steroid metabolism is directly involved in hormone action or whether it represents stages in their detoxication and removal from the body.