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Biomedical subjects

P Hamet

Publications and source records attributed to P Hamet.

At least 271 records · Page 15Linked to original sources
PubMed1979

Antihypertensive efficacy of propranolol given twice daily.

The therapeutic efficacy of propranolol in four and two daily doses was compared in 63 treated hypertensive patients in a multicentre trial. After 3 months of a stable diastolic blood pressure while receiving propranolol four times a day the patients were switched to a twice-a-day regimen, the drug being given at 8 am and 8 pm, with the same total daily dose, for 3 more months. Blood pressures and heart rates were measured at 8 am, 12 noon, 4 pm and 8 pm at 4-week intervals. There were no significant changes in mean blood pressure after the change to the twice-a-day regimen, although some patients reported new side effects. Compliance appeared to be unaffected.

Adolescent↗
PubMed1978

Characteristics of adenylate cyclase activity in pig coronary arteries.

Characteristics of adenylate cyclase activity of the intima plus media layer of pig coronary arteries have been studied. Enzyme activity in the 10,000 xg particulate fraction was linear with respect to time and protein during short incubations. Linear kinetics were observed for MgATP as a substrate and free Mg2+ as an activator. Mn2+ added in excess of ATP concentrations was only slightly stimulatory or inhibitory. Adenosine, GTP and GPP(N)P inhibited enzyme activity. Adenosine decreased the Vmax and the Ka for Mg2+ but had no effect on the Km for MgATP. The inhibition by adenosine was reversible, while that by GPP(N)P appeared to be irreversible. Although preincubation of the enzyme with GPP(N)P for short times caused irreversible inhibition, preincubation for more than 15 min caused up to 3-fold activation. Isoproterenol added to the incubation produced no or very slight stimulation with or without GPP(N)P or GTP, and preincubation with isoproterenol alone caused irreversible inhibition. However, preincubation with isoproterenol plus GPP(N)P for 30 min caused irreversible activation exceeding that observed with GPP(N)P alone. These observations suggest that vascular adenylate cyclase, like the enzyme from the other tissues, can exist in multiple states of activity and responsiveness.

Adenosine↗
PubMed1977

Renal vein plasma adenosine 3',5'-cyclic monophosphate in renovascular hypertension.

The concentration of plasma adenosine 3',5'-cyclic monophosphate (cyclic AMP) and plasma renin activity (PRA) were measured concomitantly in blood from both renal veins and in arterial blood in 22 hypertensive patients. In the nine patients with true renovascular hypertension the concentration of plasma cyclic AMP was greater in the venous effluent of the kidney affected by the renal artery stenosis than in that of the unaffected or less affected kidney. The arteriovenous difference in cyclic AMP concentration was less on the affected side in all but one patient. The arteriovenous differences in PRA identified the affected kidney as the source of hyper-reninemia and showed that renin release from the other kidney was suppressed. In the 13 patients with hypertension associated with but unrelated to renal artery stenosis there were no consistent patterns of cyclic AMP concentration or PRA in the venous effluent of the kidneys or of their arteriovenous differences. In renovascular hypertension the venous effluent of the kidney affected by renal artery stenosis contains not only more renin but also more cyclic AMP, owing to either increased cyclic AMP production or decreased excretion or extraction of cyclic AMP by the affected kidney. This unilateral increase in cyclic AMP concentration may become a complementary diagnostic feature of true renovascular hypertension.

Cyclic AMP↗
PubMed1977

Methyl xanthine phosphodiesterase inhibitors behave as prostaglandin antagonists in a perfused rat mesenteric artery preparation.

The methyl xanthines, theophylline, caffeine and 3-isobutyl-1 methyl xanthine (MIX) inhibited the pressure responses to noradrnealine, angiotensin II and potassium ions in the isolated perfused mesenteric vascular bed of the male rat. The ID50s for inhibition of responses to noradrenaline were 1.85 mug/ml (0.83 x 10(-5) M) for MIX, 18 mug/ml (1 x 10(-4)M) for theophylline and 133 mug/ml (6.8 x 10(-4) M) for caffeine. Similar ID50 concentrations were found for responses to angiotensin II and potassium. We have previously found that substances which inhibit the three pressor agents equally may be prostaglandin (PG) synthesis inhibitors or PG antagonists. Xanthine itself, cyclic AMP and dibutyrl cyclic AMP had no inhibitory effects on the preparation up to concentrations of 10-2 M. Partial inhibition of PG synthesis by indomethacin shifted the % inhibition/log concentration curve to the left, while addition of exogenous PGE2 shifted it to the right. In preparations completely inhibited by sufficient indomethacin added to the perfusate to block PG synthesis, and then restored by adding 1 or 5 ng/ml PGE2 in addition to the indomethacin, the methyl xanthines again inhibited responses suggesting that they were PG antagonists rather than inhibitors of synthesis or release. In preliminary experiments MIX also inhibited effects of PGF2alpha on rat uterus and PGE1 on guinea pig ileum. Effective concentrations of theophylline were similar to the therapeutic levels in human plasma. PG antagonists may be a major action of methyl xanthines requiring reinterpretation of many experiments which have attributed their effects to PDE inhibition. PGs may also be involved in regulating PDE action.

Angiotensin II↗
PubMed1977

Catecholamines, cyclic AMP and renin in two contrasting forms of essential hypertension.

Essential hypertension (EH) can be subdivided according to the sympathetic and renin activity into two contrasting forms: (1) borderline beta-hyperadrenergic renin hyperresponsive and (2) stable beta-hypoadrenergic renin hyporesponsive EH. These two forms probably represent two expreme poles in the spectrum of EH in which sympathetic and renin hyper- or hyporeactivity cannot be accounted for by catecholamine determinations solely. beta-Adrenergic responsiveness monitored by plasma cyclic AMP determinations revealed plasma cyclic AMP, renin and circulatory hyperresponsiveness to isoproterenol in borderline hyperadrenergic EH while the opposite, cyclic AMP and renin hyporesponsiveness to insulin-induced hypoglycemia have been described in low renin stable EH. The kidney is in the center of the adrenergic abnormality in the two forms of EH with the borderline one excreting into the urine catecholamines not accounted for by their glomerular filtration. Catecholamines solely, however, do not account for the differences in both forms of EH which can probably be attributed to their different beta-adrenergic responsiveness.

Adrenergic beta-Antagonists↗
PubMed1976

Contrasting effects of hypoglycemia on plasma renin activity and cyclic adenosine 3',5'-monophosphate (cyclic AMP) in low renin and normal renin essential hypertension.

Insulin-induced hypoglycemia previously has been shown to provoke a beta-adrenergic response that normally results in an increase in plasma renin activity (PRA). In our study, hypoglycemia induced definite increases in PRA in a group of five patients with normal renin essential hypertension but failed to do so in a group of six patients with low renin essential hypertension. In both groups, plasma cyclic adenosine 3',5'-monophosphate (cyclic AMP; cAMP) increased more than 2-fold during hypoglycemia, but the response in the low renin group was significantly less than that previously observed in normal subjects under the same conditions. Plasma cortisol increased to an equal extent in both groups of hypertensive patients during hypoglycemia. Infusion of the phosphodiesterase inhibitor, theophylline, resulted in definite increases of PRA in patients with normal renin hypertension but not in patients with low renin hypertension. Because changes in the level of plasma cAMP during hypoglycemia have been thought to reflect adrenal catecholamine release, our finding of a blunted increase in plasma cAMP during hypoglycemia in patients with low renin hypertension may suggest that there is a generalized alteration in adrenergic responsiveness in this condition.

Adrenal Medulla↗
PubMed1976

Plasma cyclic adenosine 3':5'-monophosphate response to isoproterenol and glucagon in hyperkinetic borderline (labile) hypertension.

The hemodynamic changes observed in patients with the "hyperkinetic" form of borderline (labile) essential hypertension (BEH) could be related to the hyperresponsiveness of cardiac beta-adrenergic receptors to catecholamines. The isoproterenol-induced increase in plasma cyclic adenosine 3':5'-monophosphate (cAMP) reflects the response of adenylate cyclase to beta-adrenergic stimulation, whereas a non-beta-receptor-mediated increase occurs with the administration of glucagon. Both substances were infused into 13 control subjects and 14 patients with the hyperkinetic form of BEH before and after propranolol administration. Baseline plasma cAMP concentrations were comparable in both groups. After 30 minutes of isoproterenol infusion (20 ng/kg per min) a significantly higher increase in plasma cAMP and heart rate and a smaller decrease in diastolic blood pressure were seen in this type of BEH than in control subjects. The increase in plasma cAMP and in heart rate correlated positively when all subjects were considered together. Propranolol abolished hemodynamic and humoral responses to a similar degree in both groups. The plasma cAMP responses to glucagon (200 ng/kg per min) were slightly lower in our patients with BEH than in control subjects and were not suppressed by propranolol. The data are compatible with a hyperreactivity of the beta-adrenergic receptors or of the adenylate cyclase or both in hyperkinetic BEH and could correspond to the previously observed exaggerated beta-adrenergic drive to the heart in this type of hypertension. The non-beta-receptor-mediated rise in plasma cAMP (glucagon), however, remains comparable in control subjects and BEH.

Adult↗
PubMed1976

Effects of beta-adrenergic blockade on plasma cyclic AMP and blood sugar responses to glucagon and isoproterenol in man.

In healthy humans glucagon infusion resulted in a significant increase in blood sugar and in plasma cyclic AMP. No discernible hemodynamic effects were found. Isoproterenol infusion on a mole per mole basis in the same subjects induced a significant, although less pronounced rise in plasma cyclic AMP, heart rate, and a fall in diastolic blood pressure but had no effect on blood sugar. Propranolol administration abolished the hemodynamic effects of isoproterenol and significantly decreased the response of plasma cyclic AMP; the same blocking dosage had little effect on plasma cyclic AMP changes induced by glucagon wheras the response in blood sugar was significantly reduced. These data in vivo are compatible with the in vitro demonstration of separate receptors for glucagon and isoproterenol.

Adult↗
PubMed1975

Liver membrane adenylate cyclase. Synergistic effects of anions on fluoride, glucagon, and guanyl nucleotide stimulation.

Some effects of salts on the adenylate cyclase of partially purified plasma membranes from rat liver have been studied. Under conditions where cyclic adenosine 3':5'-monophosphate formation was linear with respect to time and protein concentration, the enzyme was stimulated 3- to 6-fold by 10 mM NaF, 10- to 30-fold by 1 muM glucagon, 4- to 5-fold by 0.1 mM 5'-guanylylimidodiphosphate, and in the presence of 3 muM GTP, 2-fold by 10 mug/ml of prostaglandin E1. Various salts were found to stimulate basal activity slightly, but enhanced the response to NaF 3- to 4-fold, to glucagon 1.5- to 2-fold, to 5'-guanylylimidodiphosphate 2- to 3-fold, and to prostaglandin E1 1.5-fold. This enhancement was observed at maximally effective concentrations of each of the respective activators. Of the salts tested, NaN3 and the Na- or K-halides were most effective. Their action appeared to be due to the respective anions. Stimulation was detectable with 1.5 mM NaN3 or 3 mM NaCl and was maximal with 30 mM NaN3 or 60 mM NaCl. The stimulatory effect of NaN3 was not due to ATP-sparing, nor to an altered cyclic adenosine 3':5'-monophosphate recovery. It was independent of the chromatography and assay methods used, and was therefore not due to procedural artifact. Fluoride-stimulated cyclase activity was enhanced by salts to a greater degree than were 5'-guanylylimidodiphosphate-, glucagon-, or (prostaglandin E1 + GTP)-stimulated activities. The effects of NaN3 were not the result of significant changes in the enzyme's responses to GTP, which increased basal and glucagon-stimulated activities but inhibited F--stimulated activity. The effects of NaN3 were greater when cyclase was assayed with Mn2+ than with Mg2+. The facilitatory effect of NaN3 or NaCl on fluoride-stimulated adenylate cyclase activity was partially reversible as was the stimulatory effect of fluoride in the presence of NaN3. Enhancement of hormonal stimulation by NaN3 was also demonstrable with cardiac and adipose tissue adenylate cyclase. However, NaN3 did not stimulate detergent-dispersed adenylate cyclases from either liver plasma membranes or brain. The data suggest that stimulation of adenylate cyclase by salts may require the added presence of other stimulatory agents and an intact membrane structure.

Adenosine Triphosphatases↗
PubMed1975

Effect of hypoglycemia on extracellular levels of cyclic AMP in man.

This study was designed to assess the response of cyclic AMP to "endogenous" hormonal stimulation resulting from insulin-induced hypoglycemia. Insulin was administered to four normal subjects and four adrenalectomized patients. Hypoglycemia resulted in four-fold increases in plasma cyclic AMP. This response is thought to be secondary to beta-adrenergic stimulation for the following reasons: (1) the response was absent in adrenalectomized, cortisol-treated subjects; (2) it was abolished by propranolol; and (3) urinary excretion of cyclic AMP did not reflect the rise in plasma cyclic AMP.

Adrenal Glands↗