Intracellular pH and buffering power measured in isolated single cells from pregnant rat uterus.

Intracellular pH (pHi) affects smooth muscle function yet there have been few direct pHi measurements. Using the fluorescent indicator, 2',7'-bis-2-(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester, we report here the first measurements of pHi and buffering power (beta) in single, isolated, uterine smooth muscle cells. Mean pHi in cells from pregnant rat uteri was 7.09 +/- 0.08 (+/- S.E.M., n = 16 cells; 37 degrees C), and beta was found to be 12.8 +/- 2.8 mmol/l per pH unit (n = 15). The cells were able to regulate their pHi in the presence of butyrate when perfused in nominally CO2-free solution.

The effects of pH changes on human and ferret detrusor muscle function.

1. The effects of altering extracellular pH on the electrically evoked contractions of ferret and human bladder (detrusor) smooth muscle have been investigated. pH was varied by changing superfusate PCO2 or NaHCO3 concentration. Acidosis increased force when superfusate PCO2 was raised but decreased force when the NaHCO3 concentration was reduced. 2. Intracellular pH (pHi) in isolated ferret detrusor cells was measured separately by epifluorescence microscopy. Extracellular pH changes caused by altering superfusate PCO2 were accompanied by similar changes of pHi, whereas variation of the NaHCO3 concentration had smaller effects on pHi. 3. It was proposed that intracellular acidosis increased contraction but extracellular acidosis depressed contraction. 4. Other interventions, such as addition and removal of NH4Cl, Cl- replacement, and NaHCO3 replacement with HEPES, changed pHi and had predictable effects on force. It was possible to describe unique relationships between tension and either intracellular or extracellular pH regardless of the means whereby pH changes were brought about. 5. Resting tension was reduced whether brought about by either intracellular or extracellular acidosis. K+ contractures were similarly affected by acidosis. Ferret preparations showed low levels of spontaneous activity, which was reduced by acidosis and enhanced by alkalosis.

Clinical, autonomic and therapeutic observations in two siblings with postural hypotension and sympathetic failure due to an inability to synthesize noradrenaline from dopamine because of a deficiency of dopamine beta hydroxylase.

A brother and sister with long-standing symptoms of postural hypotension are described. They were considerably worse in the morning, after exercise and in warm weather. In the male, erection was unaffected but ejaculation was prolonged or absent. Both had nocturia, but there were no urinary bladder, bowel or sweating abnormalities. Autonomic function tests confirmed sympathetic adrenergic failure with spared sympathetic cholinergic and intact parasympathetic function. There were no other neurological abnormalities. Noradrenaline and adrenaline were undetectable in the plasma, but plasma dopamine was elevated. Urinary levels of noradrenaline and adrenaline metabolites were below detection limits, but dopamine metabolites were normal or elevated. Dopamine beta-hydroxylase activity was undetectable in the plasma. Immunohistochemical studies of perivascular cutaneous tissue confirmed normal peptidergic and tyrosine hydroxylase immunoreactivity, with absent dopamine beta-hydroxylase immunoreactivity. The findings were consistent with an enzymatic deficit in the conversion of dopamine to noradrenaline. The parents were clinically and biochemically normal. Treatment of both patients with the synthetic amino acid, d-l-threo-dihydroxyphenylserine, which contains a hydroxyl group and is converted to noradrenaline by dopa-decarboxylase, reduced symptoms and signs of postural hypotension and increased levels of plasma noradrenaline and its urinary metabolites. In the male, ejaculation became possible. Behavioural changes included a feeling of confidence and optimism, with a tendency to be argumentative. The laevo isomer also raised blood pressure and plasma noradrenaline levels. The drug had no direct pressor effects, as its actions were prevented by the dopa-decarboxylase inhibitor, carbidopa.

Renin and angiotensin converting enzyme concentrations in the fetal and neonatal guinea-pig.

1. Plasma renin concentration (PRC) and plasma and pulmonary angiotensin converting enzyme (ACE) concentration were measured in fetal and neonatal guinea-pigs from 45 days gestational age (GA) until 21 days post-partum. 2. Fetal PRC increased towards term to reach values greater than those measured in normal adult males. Pentobarbitone anaesthesia of the mother resulted in significant elevation of fetal PRC after 66 days GA but not before this time. 3. PRC were very high in the newborn guinea-pig, decreased rapidly during the first 24 h after birth and then more gradually, to reach approximately adult values by day 21. 4. Fetal plasma ACE concentration increased towards term to reach values greater than those measured in adult males and decreased subsequently. 5. Pulmonary ACE concentrations were very low throughout gestation but increased considerably between days 3 and 14 post-partum. Low concentrations of ACE were measured in other fetal tissues but placental concentrations were relatively high. 6. Propranolol (0.1 mg I.P.) or saline was administered (under halothane-nitrous oxide anaesthesia) to fetuses of litters of various GA from 55 days to term. Fetal PRC were measured 3 h later. Propranolol treatment resulted in significantly lower fetal PRC than saline treatment in litters aged 63 days to term but not in younger litters. 7. These data indicate that the renin-angiotensin system is functional in the fetal guinea-pig during the last third of gestation. Fetal plasma renin concentrations near term are greater than those measured in normal adult males. This may, in part, reflect an increased influence of the fetal sympathetic nervous system.

Prevention of glucose-induced hypotension by the somatostatin analogue octreotide (SMS 201-995) in chronic autonomic failure: haemodynamic and hormonal changes.

1. The haemodynamic and hormonal changes following glucose ingestion (1 g/kg) were determined before and after pretreatment with either placebo or the somatostatin analogue, octreotide (SMS 201-995, 50 micrograms subcutaneously), in seven patients with chronic autonomic failure. 2. In the placebo phase, after glucose, there was a marked and prolonged fall in blood pressure with no change in cardiac index and peripheral blood flow. Plasma insulin and neurotensin levels increased, whereas glucagon, vasoactive intestinal polypeptide, noradrenaline and adrenaline levels were unchanged. 3. Octreotide transiently raised blood pressure and prevented glucose-induced hypotension. There were no changes in cardiac index or peripheral blood flow. Plasma insulin and neurotensin levels did not rise. Plasma glucose levels increased more slowly but reached a similar level to the placebo phase. 4. We conclude that in autonomic failure patients, glucose-induced hypotension was not accompanied by changes in cardiac index or peripheral blood flow, indicating a lack of compensation to probable splanchnic vasodilatation. The hypotension was prevented by the peptide release inhibitor, octreotide, with no change in cardiac index or in peripheral blood flow, suggesting an effect on the splanchnic vasculature, probably through inhibiting release of vasodilatatory pancreatic and gut peptides.

Relationship between splanchnic vasodilation and postprandial hypotension in patients with primary autonomic failure.

The haemodynamic responses to a standard liquid meal were measured in patients with autonomic failure and in normal subjects. Resting superior mesenteric artery blood flow was similar in both groups, but mean supine arterial pressure and the superior mesenteric artery vascular resistance were higher in the patients with autonomic failure than in the normal subjects. After the meal there was a rise in superior mesenteric artery blood flow and a fall in superior mesenteric artery vascular resistance in both groups. Mean arterial blood pressure fell substantially after food in the patients with autonomic failure but not in the normal subjects. The basal heart rate, stroke distance and cardiac index were higher in the patients with autonomic failure, and rose significantly after the meal only in the normal subjects. Forearm blood flow fell and the vascular resistance rose after the meal in the normal subjects but not in the patients with autonomic failure. We conclude that superior mesenteric artery blood flow rose and superior mesenteric artery vascular resistance fell after the meal in the normal subjects and in the patients with autonomic failure. However, in the normal subjects the blood pressure was maintained by factors which include a rise in the heart rate and cardiac output. The lack of such compensatory changes probably accounts for postprandial hypotension in patients with autonomic failure.

Angiotensin converting enzyme inhibition lowers blood pressure in patients with primary autonomic failure independently of plasma renin levels and sympathetic nervous activity.

The haemodynamic and neurohormonal responses to the angiotensin converting enzyme (ACE) inhibitor captopril were studied in 12 patients with primary autonomic failure; seven had multiple system atrophy and five had pure autonomic failure. Basal supine mean arterial blood pressure was higher in the patients with multiple system atrophy than in those with pure autonomic failure and the normal subjects. Basal plasma noradrenaline levels were normal in the patients with multiple system atrophy, but lower in those with pure autonomic failure. Captopril lowered the mean arterial pressure in the patients with multiple system atrophy and pure autonomic failure but not in the normal subjects. In the patients with multiple system atrophy and pure autonomic failure, captopril lowered the cardiac output and the stroke volume. Forearm vascular resistance was unchanged. No significant changes occurred in the normal subjects. Plasma renin activity was unchanged after captopril in the patients with autonomic failure, but rose in the normal subjects. Plasma noradrenaline was unchanged in all groups after the administration of captopril. We conclude that captopril lowers the mean arterial pressure in patients with multiple system atrophy and pure autonomic failure. After the administration of captopril there is a reduction in cardiac output, secondary to a fall in stroke volume. The vasodepressor response to captopril in patients with autonomic failure is not related to the basal level of plasma renin activity or sympathetic nervous activity, indicating that the hypotensive effects of bradykinin or prostaglandins, or both, may contribute.