Vascular hypertrophy in renal hypertensive spontaneously hypertensive rats.

Vascular smooth muscle cells isolated from spontaneously hypertensive rats (SHR) replicate faster in vitro than do cells from Wistar-Kyoto (WKY) rats, suggesting that the vascular hypertrophy seen early in the life of SHR might be at least partially caused by abnormal cellular growth properties in vivo. To test whether specific growth stimuli produce more extensive hypertrophy in SHR than WKY rats, we compared their cardiovascular growth responses to two-kidney, one clip renal hypertension. Six-week-old animals were subjected to either renal artery clipping or sham operation. Four weeks after renal artery clipping, there was a proportionately smaller rise in systolic blood pressure in SHR than WKY rats (21% and 44%, respectively); however, the overall level of systolic blood pressure achieved in the two rat strains differed by less than 10 mm Hg (4%). Limitations in the blood pressure responses of SHR to renal artery clipping were not due to inadequate development of left ventricular hypertrophy, as this was greater in SHR than WKY rats; however, aortic hypertrophy was similar in both strains. Aortic DNA content changes in SHR were consistent with a significant hyperplasia of medial smooth muscle cells, whereas in WKY rats, there was cellular hypertrophy. Small and medium-sized arteries of the mesenteric vasculature were also hypertrophied in SHR, and the medial cross-sectional area increased by 63% and 114%, respectively, compared with increases of only 15% and 23% in WKY rats. Strain differences between the sham-operated rat groups were small.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic angiotensin II type 1 receptor antagonism in genetic hypertension: effects on vascular structure and reactivity.

OBJECTIVE AND DESIGN: The aim of the study was to assess the role of angiotensin II (Ang II) in the maintenance of cardiovascular hypertrophy and the abnormal vascular amplifier properties in spontaneously hypertensive rats (SHR) with established hypertension. Losartan, a type 1 Ang II receptor antagonist, was administered to SHR and Wistar-Kyoto (WKY) rats, and its effects on blood pressure, cardiac hypertrophy, vascular morphology and hindquarter vascular amplifier properties assessed at the end of treatment and 3 months later. METHODS: Losartan was administered for 6 weeks to 14-week-old SHR (60 mg/kg per day orally). A bio-equivalent dose (20 mg/kg per day orally) was administered to age-matched WKY rats. Systolic blood pressure (SBP) was measured in conscious rats by tail-cuff plethysmography. Morphological changes were assessed both in the heart, from the ratio of the weight of the left ventricular wall plus septum to body weight, and in blood vessels from the medial cross-sectional areas of the abdominal aorta and mesenteric arteries. Vascular amplifier properties were measured by perfusion of the rat hindquarters under conditions of full dilation (papaverine hydrochloride) and incremental constriction with methoxamine hydrochloride. RESULTS: Losartan lowered SBP in SHR to normotensive WKY rat levels during treatment. Left ventricular hypertrophy and aortic cross-sectional area were reduced at the end of treatment to WKY rat levels; mesenteric artery cross-sectional area was reduced to a lesser extent. The abnormal hindquarter vascular amplifier properties of the SHR were normalized by losartan. Three months after treatment ended, SBP had returned to untreated SHR levels. Left ventricular hypertrophy and the abnormal hindquarter vascular amplifier properties had also partially redeveloped. CONCLUSIONS: Our findings support the hypothesis that Ang II contributes to the maintenance of cardiovascular hypertrophy and the abnormal vascular amplifier properties in SHR with established hypertension. However, its role appears to be variable and to depend on the type of vascular bed. Other, pressure-independent, factors may also contribute to vascular hypertrophy.

Plasma renin activity and blood corticosteroids in the Australian lungfish Neoceratodus forsteri.

Plasma renin activity (PRA) and blood aldosterone and deoxycorticosterone levels were measured in Australian lungfish. Plasma renin activity was depressed after intravenous infusions of iso-osmotic (0-6%) NaCl but not after hypo-osmotic (0-3%) infusions. The presence of PRA in this fish is consistent with prior reports of renal renin activity in other sarcopterygian fishes. The results of the infusion experiments suggest that a fall in plasma osmolality or electrolyte concentrations may oppose the reduction in renin release in response to volume expansion. Aldosterone and deoxycorticosterone were identified in the blood of Neoceratodus. The concentrations of both appeared higher in females than in males. Infusions of [5-valine]-angiotensin II amide for 2-4 h at rates known to increase blood pressure in this species did not alter blood aldosterone concentrations. This negative finding may suggest that the renin/angiotensin system is not involved in aldosterone regulation in Neoceratodus or that angiotensin receptors involved in regulation of steroidogenesis have a greater specificity for endogenous angiotensin than do vascular receptors.

Blood corticosteroids in Australian marsupial and placental mammals and one monotreme.

Peripheral blood corticosteroid levels were determined in nine species of Australian marsupial (Eastern grey kangaroo, black-tailed, Bennett's and pademelon wallabies, quokka, wombat, koala and Western native and tiger cats), one species of monotreme (echidna) and one placental Australian mammal (dingo). Animals were obtained or bled with minimal disturbance and came from areas considered to have adequate sodium content of the vegetation. Aldosterone, corticosterone, cortisol, 11-deoxycorticosterone and 11-deoxycortisol were measured and levels found to be similar to five introduced eutherian species (sheep, cow, dog, fox and man) with the exception of the koala and the wombat. Cortisol was the predominant corticosteroid, except in the koala, which produced corticosterone in relatively the greatest quantity, and the wombat which produced more 11-deoxycortisol. Steroid levels were generally low in the wombat. ACTH administered to the koala changed its pattern of corticosteroid secretion from predominantly corticosterone to cortisol. In the dingo, administration of ACTH caused rises in corticosteroid levels similar to those seen in most other eutherian mammals.

The effects of ACTH on adrenal steroidogenesis and blood corticosteroid levels in the echidna (Tachyglossus aculeatus).

1. The effects of short-term (S.T., 30 min) and long-term (L.T., 4 days) administration of ACTH on peripheral blood corticosteroid levels and on in vitro steroidogenesis were investigated. 2. Control levels of cortisol, corticosterone and aldosterone were 58 +/- 12, 130 +/- 26 and 10 +/- 6 (SEM) ng/100 ml respectively. 3. Corticosterone was 70% higher after S.T. and 150% higher after L.T., when cortisol was 800% higher. 4. Adrenal homogenates from control echidnas converted [14C]progesterone predominantly to 11-deoxycorticosterone (45%) and 11-deoxycortisol (12%). 5. After L.T. the principal product was corticosterone (25%), but S.T. had no effect. 6. In control echidnas the Km and V for 11 beta-hydroxylation of 11-deoxycorticosterone were 20 microM and 2.8 rho mol/min/mg respectively. After L.T. V increased to 10 rho mol/min/mg.

Long-term angiotensin II antagonism in spontaneously hypertensive rats: effects on blood pressure and cardiovascular amplifiers.

1. The angiotensin II type 1 receptor antagonist, losartan, prevented the development of hypertension in spontaneously hypertensive rats (SHR). 2. Losartan also prevented the development of left ventricular hypertrophy and vascular amplifier abnormalities. 3. Part of the hypotensive effect induced by long-term treatment with losartan persisted for a long time after the withdrawal of treatment. 4. The results support the hypothesis that angiotensin II contributes to the development of hypertension and cardiovascular hypertrophy in SHR.

Factors in the control of plasma renin activity and concentration in Type 1 (insulin-dependent) diabetes.

Possible factors involved in the control of plasma renin activity (PRA) and concentration (PRC) have been analysed in 49 patients with long-standing Type 1 diabetes and in 40 healthy controls matched for age and sex. Eighteen of the diabetic subjects were clinically free of all microvascular and macrovascular complications of their disease (Group A); 31 had proliferative retinopathy (Group B). Both lying and standing PRA and PRC were similar in Group A and healthy controls. Mean PRA was 50-115% higher in Group B diabetics than in controls (P less than 0.001 supine and erect) and 50-70% higher than in Group A diabetics (P less than 0.05 supine and erect); PRC also was 60% higher in Group B than in Group A (P less than 0.05 supine and erect). Control subjects showed significant falls in both PRA and PRC with increasing age, while Groups A and B showed significant falls in PRA or PRC with age. Group A showed a significant inverse correlation between systolic blood pressure and supine PRC (r = -0.57), but this was not significant in the controls and was completely absent in Group B. With correction for the effect of age there were significant relationships of PRA and PRC with sodium excretion in the controls and in Group A, but not in Group B. PRA and PRC are thus normal in uncomplicated long-standing Type 1 diabetes, but regulation of renin secretion appears to be impaired in patients with microvascular disease. Renin secretion inappropriate to their blood pressure and sodium status may contribute to maintenance of their relative hypertension.

High-performance liquid chromatographic analysis of norepinephrine and alpha-methylnorepinephrine in microdissected noradrenergic cell groups of the rabbit brain.

A high-performance liquid chromatographic method with electrochemical detection has been developed to measure norepinephrine (NE) and alpha-methylnorepinephrine (alpha-MeNE) in microdissected noradrenergic cell groups of the rabbit brain stem. The method is shown to be specific, accurate and precise and has a sensitivity of 0.5 pmol per sample. The method has been applied to the measurement of NE and alpha-MeNE levels in the A1, A2, A5, A6 and A7 noradrenergic cell groups after administration of the antihypertensive drug alpha-methyldopa (alpha-MD), so that the sites of action of alpha-MD within the central nervous system may be localised.

Development and application of a superfusion technique for the study of renin secretion in rat renal cortical cells.

A dynamic column superfusion system has been developed for the study of renin secretion in rat renal cortical cells. Cells were isolated by collagenase digestion and mechanical dispersion, before suspension with polyacrylamide beads and superfusion with oxygenated physiological medium. Renin was detected in the superfusate by incubation of fractions with excess nephrectomized sheep substrate in the presence of angiotensinase inhibitors followed by radioimmunoassay of the angiotensin I generated. Optimized methodology included a purpose-built polytetrafluorethylene flow cell, a 1 h equilibration to achieve a steady state, 5 min eluate collections, a 15 min stimulatory and a 30 min recovery period, and duration of perfusion of up to 270 min. Significant increments above baseline renin release were seen with the stimuli of adrenaline, noradrenaline and isoprenaline. These could be demonstrated with concentrations of 10(-9) mol/l (adrenaline), 5 X 10(-10) mol/l (noradrenaline) and 10(-9) mol/l (isoprenaline). This technique has significant advantages over previous methods for the study of renin secretion in vitro at the cellular level. It is reproducible and sensitive, and avoids many of the limitations of static cell suspension and kidney slice methods.

Hypertension due to 17alpha-hydroxylase deficiency.

A female patient with hypertension, hypogonadism and hypokalaemia due to 17alpha-hydroxylase deficiency is described, in whom the diagnosis was initially based on the finding of low urinary 17-ketosteroids and 17-hydroxycorticosteroids, in the presence of high plasma fluorometric 11-hydroxycorticoids. Later studies confirmed the diagnosis by demonstrating low circulating levels of 17alpha-hydroxyprogesterone and the steroids derived from this precursor: 11-deoxycortisol, cortisol, oestradiol and testosterone. Plasma progesterone, corticosterone and deoxycorticosterone (DOC) were greatly increased, but plasma and urine aldosterone were very low. The initial subnormal cortisol and 11-deoxycortisol levels responded to tetracosactrin administration, suggesting that the adrenal was not maximally stimulated by endogenous ACTH and indicating that the 17alpha-hydroxylase deficiency was incomplete. Plasma and urinary aldosterone levels were still suppressed after 12 months treatment with prednisone despite normalization of the previously suppressed renin levels. The findings indicate that this uncommon cause of medically-controllable juvenile hypertension can be identified without specific steroid assays.

A sequential study of adrenocorticosteroid level in human pregnancy.

1. Peripheral plasma levels of aldosterone, corticosterone, cortisol, 11-deoxycorticosterone (DOC) and 11-deoxycortisol were measured sequentially throughout pregnancy in eleven women. 2. Mean plasma concentrations were significantly increased above non-pregnant values at 8 weeks for DOC, at 12 weeks for corticosterone, cortisol and 11-deoxycortisol, but not until 24 weeks for aldosterone. 3. It is suggested that during human pregnancy, the maternal adrenal is responding differently to corticotrophin, pituitary or placental, and that other factors, for example prolactin, may be stimulating the adrenal directly or modifying the action of corticotrophin.

Effect of autonomic blockade on the hemodynamic responses of normal human subjects to acute intravenous milrinone.

We studied the hemodynamic effects of four doses of milrinone, administered by intravenous (i.v.) infusion alone and after autonomic blockade with prazosin, propranolol, atropine, and clonidine. Plasma concentrations of milrinone (50-600 ng/ml) were similar to those used for the treatment of cardiac failure and were unaltered by autonomic blockade. When given alone, milrinone induced dose-dependent increases in heart rate (maximum increase 21 +/- 4, SEM, beats/min) and cardiac output (CO) (maximum 44 +/- 9%) and reduced systemic vascular resistance (SVR) by a maximum of 32 +/- 5%. After autonomic blockade, milrinone caused a similar fall in SVR and a smaller but significant (7 +/- 2 beats/min) rise in heart rate, but no change in CO. The increase in CO produced in normal humans by acute i.v. infusions of milrinone depends on intact cardiovascular reflexes.

Effect of intravenous infusion of corticosteroids on blood pressure, electrolytes, and water metabolism in sheep.

ACTH administration (80 IU/day for 5 days), which produces hypertension and charateristic metabolic effects in sheep (38), has been compared with the effect of intravenous infusion of cortisol (5 mg/h), corticosterone (0.5 mg/h), deoxycorticosterone (50 mug/h), and 11-deoxycortisol (1 mg/h), each given singly for 5 days. Further, a mixture consisting of aldosterone (3 mug/h), cortisol (5 mg/h), deoxycorticosterone (25 mug/h), corticosterone (0.5 mg/h), and 11-deoxycortisol (1 mg/h), was also infused intravenously for 5 days. In another series of experiments, 18-hydroxydeoxycorticosterone (100 mg/h) was also included in the combined-steroid solution. With the exception of 18-hydroxydeoxycorticosterone, which was not measured, the rates of infusionproduced peripheral arterial blood levels of the steroids similiar to those seen with ACTH stimulation. Blood pressure,water intake, urine output, and plasma and urinary electrolytes were measured: individual steroids had little effect on these, but manyof the metabolic changes produced by ATCH (hypokalemia and increased water intake andurine output) were produced by the combined-steroid infusion. However, the combined-steroid infusion failed to induce an increase in blood pressure similiar to that seen inthe ACTH experiments. Thus the findings are against a major role in ACTH hypertension for any steroid used, either singly or in combination. As yet unrecgnized factor/s may be involved in the ACTH-induced hypertension.

Increased plasma renin activity in type 1 diabetes with microvascular disease.

Plasma renin activity was measured in thirty-one subjects with Type 1 diabetes and proliferative retinopathy, and in seventeen matched diabetic subjects without evidence of any complications of their disease. The two groups were comparable for age, sex, smoking habits and duration of diabetes. Systolic and diastolic blood pressures were significantly higher in the patients with retinopathy (P less than 0.025 and P-0.05 respectively) and HbA1 was greater (P less tha 0.005) than in the patients without complications. Plasma renin activity, both lying and standing, was higher in the patients with retinopathy than in the uncomplicated group (P less than 0.05 for each). There were no correlations between plasma renin activity and mean blood pressure, HbA1 or fasting blood glucose. These findings raise the possibility that the renin-angiotensin system might be implicated in the pathogenesis of diabetic microvascular.

The ontogeny and regulation of corticosteroid secretion by the ovine foetal adrenal.

Adrenal glands of foetal sheep of 40 days gestation to term were incubated with and without ACTH or an increased [K-+]. With ACTH, the 40 day foetal adrenal was capable of producing more cortisol and aldosterone per g body weight than was the term adrenal. ACTH was a potent stimulus to aldosterone and cortisol production in foetuses aged 60-90 days, and this effect declined significantly in the 91-120 day period. An increased [K-+] was stimulatory to aldosterone production only after 120 days gestation. Peripheral blood levels of aldosterone, corticosterone, cortisol, 11-deoxycortisol and 11-deoxycorticosterone were measured in foetuses 60 days to term and the levels of aldosterone and cortisol were significantly lower in 90-120 day foetuses than in the younger or older ones. Direct adrenal vein cannulation proved all five steroids to be secretory products of the foetal adrenal.

Biosynthetic ad morphological evidence for inhibition of aldosterone production following administration of ACTH to sheep.

The effect of ACTH administration for 1-5 days on the morphology and steroidogenic capability of sheep adrenal tissue has been examined. During this period of treatment there was a gradual decline in the in vitro conversion of 3H-labelled precursors to products of solely zona glomerulosa origin (aldosterone and 18-hydroxycorticosterone) while conversion to products of zona fasciculata origin (17-hydroxyprogesterone, 11-deoxycortisol and cortisol) was stimulated throughout. Conversion to DOC, 18-hydroxydeoxycorticosterone and corticosterone (steroids produced by both the zona glomerulosa and the zona fasciculata) declined after initial stimulation. Within 2--3 days of the commencement of treatment, the zona glomerulosa showed a progressive decrease in cell number associated with disruption of cords and cell separation. Ultrastructurally, it was found that typical zona glomerulosa cells had almost disappeared. The majority of residual cells in this area had a structure intermediate between zona glomerulosa and zona fasciculata cells. The similarity in time-course of the alterations in both the morphological and biosynthetic characteristics suggests that the decline in aldosterone output caused by ACTH administration to sheep results from the loss of adrenal zona glomerulosa cells, predominantly due to selective cellular degeneration.

The effect of pregnancy on mineralo- and gluco-corticoid secretion in the sheep.

1. The peripheral blood concentrations of aldosterone, corticosterone and cortisol were measured during pregnancy in conscious, undisturbed sheep. 2. Aldosterone levels did not change during pregnancy and the mean pregnant value, 1-2 s.d. 1-4 ng/100 ml(n = 12) was not significantly different from the non-pregnant value, 2-1 s.d. 1-7 (n = 16). 3. Cortisol levels likewise were unchanged by pregnancy-non-pregnant values were 0-56 s.d. 0-50 mug/100 ml (n = 12) compared with 0-46 s.d. 0-40 mug/100 ml (n = 16) in pregnant sheep. 4. Sheep of 110-140 days gestation had a 400 mmol greater total exchangeable sodium than non-pregnant sheep. Plasma volume and plasma renin concentration tended to be elevated near to term. 5. Very high aldosterone secretion rates and peripheral blood levels could be produced in pregnant sheep by stress, intravenous ACTH or angiotensin II infusions, and by sodium deficiency. It is suggested that the pregnant sheep may show increased sensitivity in contrast to non-pregnant sheep to these stimuli and the enlarged size of their adrenals may be a contributing factor.