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Biomedical subjects

H Kather

Publications and source records attributed to H Kather.

At least 181 records · Page 10Linked to original sources
PubMed1977

Adenylate cyclase of human gastric mucosa. Stimulation of enzyme activity by histamine and catecholamines.

Human gastric mucosal adenylate cyclase has been shown to be sensitive to histamine and catecholamines. Stimulation of enzyme activity by histamine and catecholamines were selectively blocked by cimetidine and propranolol, respectively. Combination of both hormones at maximally effective concentrations were additive, indicating that human gastric mucosa contains at least two separate hormone-sensitive adenylate cyclases.

Adenylyl Cyclases↗
PubMed1977

Topographical studies on histamine- and adrenaline-sensitive adenylate cyclases in gastric and duodenal mucosa of human beings.

The distribution of histamine- and catecholamine-sensitive adenylate cyclases in human gastric and duodenal mucosa was studied. Basal enzyme activities averaged 155 pmol cAMP/mg prot./15 min in fundic gastric mucosa, 305 pmol cAMP/mg prot./15 min in the antral and 344 pmol cAMP/mg prot./15 min duodenal mucosa. 1 mM histamine induced a more than 2-fold increase of enzyme activity in fundic homogenates, whereas this secretagogue was nearly ineffective in similar preparations from the antral region (1.2-fold increase of enzyme activity). The response towards adrenaline was virtually identical in fundic and antral mucosa preparations. The duodenal enzyme was insensitive toward this catecholamine as well as to histamine. The data are suggestive for a messenger function of cAMP in histamine-stimulated gastric acid secretion.

Adenylyl Cyclases↗
PubMed1977

Adenylate cyclase of human fat cell ghosts. Stimulation of enzyme activity by parathyroid hormone.

Some of the effects of native bovine parathyroid hormone and of the synthetic aminoterminal 1-34 fragment on the adenylate cyclase activity of human fat cell ghosts were studied. Saturating concentrations of both hormone preparations caused a significant increase of enzyme activity by about 200-300%. Guanosine 5'-triphosphate (0.1 mM) inhibited basal enzyme activity but had no substantial effect on parathyroid hormone-stimulated enzyme activity. The guanosine 5'-triphosphate analogue, 5'-guanylyl-imidodiphosphate, produced about a threefold enhancement of basal and parathyroid hormone-stimulated enzyme activities under standard conditions (5 mM Mg+2, 1mM ATP, pH 8.0, 30 degrees C). Activation by parathyroid hormone was not influenced by beta-adrenergic blockade in contrast to stimulation by epinephrine. The sensitivity of the enzyme system to the native and the synthetic parathyroid hormone was, however, abolished after pretreatment of the fat cells with trypsin (1 mg/ml). The stimulatory effects of epinephrine and NaF were not affected by pretreatment with trypsin. The results suggest that human fat cells, like rat adipocytes, contain a multireceptor-coupled adenylate cyclase.

Adenylyl Cyclases↗
PubMed1977

Unchanged hormone sensitivity of rat fat cell adenylate cyclase in uremia.

The sensitivity to hormones of the fat cell adenylate cyclase system was tested in uremic rats and in pair-fed control animals. Basal enzyme activities averaged 1.25 nmoles of cAMP formed per mg protein per 15 min in controls compared to 1.30 nmoles cAMP/mg protein/15 min in fat cell ghosts obtained from uremic rats. NaF caused an approximately 4-fold stimulation of enzyme activities in both systems. It was shown that parathyroid hormone should be included amongst the hormones which act as stimulators of the enzyme system. The responsiveness of the rat fat cell adenylate cyclase system towards saturating concentrations of ACTH, glucagon, epinephrine and parathyroid hormone was not altered in the presence of chronic renal failure.

Adenylyl Cyclases↗
PubMed1977

beta-blocking agents and human fat cell adenylate cyclase.

The effects of various beta-blocking agents upon the catecholamine-activated adenylate cyclase of human fat cell ghosts were studied. Both non-selective and cardio-selective beta-blocking drugs are capable in inhibiting the human enzyme system. The concentrations of the non-selective beta-blockers (bupranolol, alprenolol, propranolol, 4-hydroxypropranolol, prindolol and oxyprenolol) required to produce half maximal inhibition of isoproterenol-stimulated rates of cAMP-formation were found to be in a narrow range (5X10(-7) M-3X10(-6) M).The cardioselective beta-blocking agents, however, were only 1/100 (methypranol) to 1/1000 (atenolol, practolol) as potent as the non-selective drugs.

Adenylyl Cyclases↗
PubMed1977

Histamine-sensitive adenylate cyclase of human gastric mucosa.

The adenylate cyclase system of human fundic gastric mucosa was found to respond to histamine, prostaglandin E 2 and the non-hormonal activators NaF and 5'-guanylyl-imidodiphosphate (GMP(PNP)). Half maximal stimulation of enzyme activity was observed at a histamine concentration of 50 micrometer. Maximal stimulation (about 25%) occurred at a histamine concentration of 1 mM. The stimulatory effect of histamine was competitively inhibited by cimetidine. The stimulatory effect of prostaglandin E 2 was found to be dose-dependent over a concentration range from 0.1 micrometer to 1 mM exerting maximal effects at 0.3 mM. NaF and GMP(PNP) by inducing an about 3.5-fold increase of enzyme activity were more potent in stimulating the human enzyme system than histamine and prostaglandin E 2. Maximal stimulatory doses of prostaglandin E 2 and histamine had an additive effect on the adenylate cyclase activity from fundic gastric mucosa. This implies that histamine acts on an individual adenylate cyclase system. Our results are suggestive for the existence of an adenylate cyclase system in human gastric mucosa coupled to histamine H 2-receptor sites.

Adenylyl Cyclases↗
PubMed1977

Adenylate cyclase of human fat cell ghosts. Stimulation of enzyme activity by prostaglandins.

It has been shown that the human fat cell adenylate cyclase is activated by prostaglandins. Of the prostaglandins tested the E-type by causing about a 3-fold increase of enzyme activity, was more effective than the F-prostaglandins. Prostaglandin A2 had no stimulatory effect. Activation by prostaglandin E1 was not influenced by beta-adrenergic blockade in contrast to stimulation by epinephrine. Pretreatment of fat cells with trypsin resulted in an abolishment of PTH-sensitivity, but had no effect on prostaglandin responsiveness. These results suggest that the human fat cell adenylate cyclase is coupled to at least three distinct types of hormone receptors.

Adenylyl Cyclases↗
PubMed1976

Membrane SH-groups related to adrenaline action in rat adipocytes: a comparative study using sulfhydryl reagents of different molecular size.

The orientation of SH-groups within the fat cell membrane involved in adrenaline (and NaF) action was studied by comparing the effects of uncoupled p-CMB with those of a large derivative of this reagent -- p-CMB-dextran --. Preincubation of intact adipocytes with uncoupled p-CMB caused a dose-dependent inhibition of adrenaline (and NaF) stimulated adenylate cyclase activity as determined in ghosts prepared subsequently. Preincubation with p-CMB-dextran, however, influenced neither the lipolytic response to adrenaline nor the catecholamine (and NaF) activated adenylate cyclase activity. When p-CMB-dextran was present during ghost preparation, a dose-dependent inhibition of adrenaline (and NaF) stimulated adenylate cyclase activity was observed. These results suggest that the binding sites of adrenaline as well as SH-groups essential for activity of adenylate cyclase are not localized near enough to the exterior surface to be accessible for p-CMB-dextran. The polarity in the sensitivity of fat cell adenylate cyclase could not be observed when p-CMB-dextran was added directly to intact or fragmented ghosts. The abbreviations used are: Cyclic AMP, cyclic adenosine 3',5'-monophosphate; p-CMB, p-chloromercuribenzoate.

Adenylyl Cyclases↗
PubMed1976

Catecholamine-sensitive adenylate cyclase of human fat cell ghosts. Characteristics of the GMP(PNP)-liganded state.

The effects of 5'-guanylyl-imidodiphosphate (GMP(PNP)) on the catecholamine-sensitive adenylate cyclase of human fat cell ghosts were studied. The compound increased basal and epinephrine-stimulated enzyme activity by about 300%; in addition GMP(PNP) increased hormone sensitivity by reducing the epinephrine concentration required, to produce half maximal stimulation. The rate of GMP(PNP)-induced activation was slow in onset and could be enhanced by epinephrine. The GMP(PNP)-activated state was resistant to thermal inactivation and could not be reversed by extensive washing. The application of this compound in clinical studies may be useful because of its stimulating and stabilizing action.

Adenylyl Cyclases↗