Calcitonin gene-related peptide and regulation of human cardiovascular homeostasis.

Isolation of calcitonin mRNA initiated studies on the multigene complex encoding a family of peptides: calcitonin, its terminal flanking peptides, calcitonin gene-related peptide (CGRP), and amylin. CGRP is expressed in alpha- and beta-forms that vary by one and three amino acids in rat and humans, respectively. Both alpha- and beta-CGRP are very similar in their biologic activities, therefore the role of duplicating the calcitonin/CGRP gene is unclear. CGRP behaves principally as a regulatory neuropeptide acting locally through interaction with target organ receptors that are either cyclic-AMP dependent, or capable of activating KATP channels of vascular smooth muscle. The dense distribution of CGRP-rich structures and the expression of mRNA in the central nervous system suggests that CGRP has a neuromodulator or neurotransmitter role not limited to vasoregulatory effects only, but like calcitonin, extends its action to physiologic, metabolic, and behavioral functions. Activation of perivascular sensory nerves stimulates the release of neuropeptides, including CGRP, which exerts a potent vasodilatory effect on venous and arterial vasculature. The increased levels of CGRP-like immunoreactivity were observed in volume overload states, in heart failure and myocardial infarction, and in some forms of hypertension. The beneficial effect of CGRP infusions was demonstrated in patients with congestive heart failure and also in subjects with neurological deficits after surgical treatment of subarachnoid hemorrhage. On the other hand, there are experimental studies on the inhibition of increased CGRP activity, in septic and shock conditions, in which the vascular hyperrelaxation could have deleterious effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered renin and aldosterone excretion in patients treated for metastatic germ cell tumours.

Twenty-four patients with metastatic germ cell tumours were studied for abnormalities in the renin-aldosterone axis and for persistent abnormalities of renal function 9+ to 54+ months following completion of cisplatin based chemotherapy. Increased plasma renin activity and aldosterone were identified in fourteen of nineteen (79%) patients. The mean serum magnesium was subnormal. Statistically lower serum phosphorus levels, and higher urea and creatinine levels were also observed. No patients was hypertensive or on diuretics at the time of study. Since vascular toxicity has been reported after cisplatin based chemotherapy and hypomagnesaemia and increased plasma renin activity have been linked to cardiovascular events, these data imply that germ cell tumour patients treated with cisplatin based chemotherapy should be carefully observed for delayed cardiovascular toxicity.

Ovarian prorenin.

We review here recent evidence that the ovaries synthesize and secrete prorenin and we explore the possible reasons why prorenin, and not active renin, is formed almost exclusively in this extra-renal site. Very high concentrations of prorenin are present in the human ovary in the fluid inside mature follicles. This ovarian prorenin appears to be secreted into the circulation since plasma prorenin increases in normal women for two to three days at mid-menstrual cycle, at the time of ovulation. No change in plasma active renin occurs at this time. Plasma prorenin increases much more at mid-cycle in women whose ovaries have been hyperstimulated with gonadotropins. Their mid-cycle increment in plasma prorenin (after hCG) is directly related to the number of ovarian follicles. Plasma prorenin also increases markedly (10-fold) in pregnant women within two weeks after conception, in parallel with the rise in endogenous hCG. The ovaries are the apparent source of the increase in plasma prorenin during pregnancy since no such increase occurred in a woman with ovarian failure who conceived after receiving a donor egg. These results suggest that the ovaries synthesize and secrete prorenin in response to stimulation by gonadotropic hormones. Future studies will investigate the potential role of ovarian prorenin in human reproductive function. We postulate the existence of a prorenin receptor which activates prorenin and, in consequence, activates a local renin-angiotensin system. The functioning of this system may be regulated by changes in prorenin and its receptor.

Increased plasma renin and aldosterone in patients treated with cisplatin-based chemotherapy for metastatic germ-cell tumors.

Twenty-four normotensive males in complete remission (CR) for 9+ to 54+ months after cisplatin-based chemotherapy for metastatic germ-cell tumors were evaluated for evidence of alterations in the renin-aldosterone axis and renal function. Abnormally high ambulatory plasma renin activity was seen in 14 of 19 patients with 24-hour urine sodium excretion greater than 50 mEq. This was correlated with elevated ambulatory plasma aldosterone (P = .009) and 24-hour urinary aldosterone excretion (P = .01). The mean serum magnesium value (1.34 +/- .05 mEq/L) was subnormal. Therapy resulted in an increase in serum creatinine during treatment (P less than .0001), an increase in BUN (P less than .01), and decrease in serum phosphorus (P less than .001). The relationship between the alterations in the renin-aldosterone axis and abnormal renal tubular function remains to be determined. In view of reports of cardiovascular toxicity after treatment for germ-cell tumors, and evidence individually linking both magnesium deficiency and increased plasma renin activity (PRA) to cardiovascular consequences, these abnormalities in renin and magnesium metabolism suggest that patients treated with cisplatin-based chemotherapy should be carefully observed for the development of delayed cardiovascular toxicities.

The captopril test for identifying renovascular disease in hypertensive patients.

To develop a screening test for identifying renovascular hypertension, the blood pressure and plasma renin activity responses to an oral test dose of captopril were studied in 246 quietly seated hypertensive patients. The following criteria were developed that exploit the hyperresponsiveness of renin secretion in renovascular hypertensive patients: a 60-minute post-captopril plasma renin activity of 12 ng/ml per hour or more and an absolute plasma renin activity increase of 10 ng/ml per hour or more, along with a 150 percent increase in plasma renin activity (or a 400 percent increase if the baseline plasma renin activity was below 3 ng/ml per hour). Retrospectively, the test identified, among 200 hypertensive patients without evidence of renal dysfunction, all 56 patients with proved renovascular disease. In this group, false-positive results occurred only in two of 112 patients with essential hypertension and in six with secondary hypertension. Nine untreated patients had blood pressure levels of less than 160/100 mm Hg. The test was neither as sensitive nor specific in the 46 patients with renal insufficiency. This study demonstrates that the renin response to oral captopril is a useful screening test for identifying patients with unilateral or bilateral renovascular disease. Since the test also characterizes the renin dependency of the hypertension, it may have other diagnostic and therapeutic uses.

Regional blood flow and neurohormonal responses to milrinone in congestive heart failure.

We measured systemic hemodynamics, regional blood flow, and neurohormonal parameters in 13 patients with severe chronic congestive heart failure before and after 1 month of therapy with oral milrinone, a bipyridine cardiotonic agent. After milrinone there were significant reductions in pulmonary wedge pressure (27 +/- 2 to 19 +/- 3 mm Hg; P less than 0.02) and systemic vascular resistance (1866 +/- 152 to 1393 +/- 93 dyne X sec/cm5; P less than 0.05) that were associated with increases in cardiac index (1.85 +/- 0.15 to 2.47 +/- 0.20 L/min/m2; P less than 0.02). There was a marked improvement in forearm blood flow (1.98 +/- 0.14 to 3.02 +/- 0.16 ml/min/dl; P less than 0.01) and a reduction in forearm vascular resistance (45 +/- 3 to 30 +/- 3 U; P less than 0.01). Overall there was no significant change in renal blow flow, renal vascular resistance, or glomerular filtration rate. However, there was a heterogeneous response of renal blood flow and glomerular filtration rate, such that both were directly correlated with the magnitude of increase of cardiac index (r = 0.587 [P less than 0.05] and r = 0.721 [P less than 0.01], respectively). After milrinone there were no significant overall or subgroup changes in urinary sodium excretion, blood volume, plasma renin activity, urinary aldosterone levels, plasma or platelet vasopressin levels, or plasma norepinephrine levels. Thus 1 month of therapy with milrinone improves systemic and forearm hemodynamics, but its effects on renal blood flow and function were heterogeneous. These heterogeneous effects on regional blood flow may depend on the relative vasodilator and inotropic effects of milrinone.

Plasma and platelet vasopressin in essential hypertension and congestive heart failure.

In this study we found that, in 31 normal subjects, close to 90% of circulating arginine vasopressin (AVP), measured by radioimmunoassay, was associated with platelets. By using routine methods of centrifugation, which do not completely separate platelets, the normal range of plasma vasopressin was higher by twofold than the normal range in platelet-free plasma prepared by differential centrifugation, which was 1.4 +/- 1.0 sd pg/ml. Platelet vasopressin was 12.9 +/- 5.7 pg/ml. Patients with congestive heart failure had, on average, an elevated platelet-free plasma AVP, as did two patients with thrombocytopenia and one with thrombocytosis. Patients with essential hypertension had slightly high levels of platelet-free plasma AVP and demonstrated an abnormal inverse relationship between platelet-free plasma AVP and serum osmolality. Immunoreactive platelet vasopressin was slightly low in patients with essential hypertension and was subnormal in patients with congestive heart failure. These studies demonstrate that platelets normally present in centrifuged plasma cause an overestimation of the plasma vasopressin levels. Until the physiological meaning of plasma and platelet-bound AVP is understood, studies of circulating vasopressin should probably assess both plasma and platelet AVP levels.

The development and application of a radioimmunoassay for dihydrodigoxin, a digoxin metabolite.

The cardioinactive digoxin metabolite, dihydrodigoxin, has been conjugated to bovine serum albumin and to bovine pancreatic ribonuclease by the periodate oxidation method. Rabbits immunized with the dihydrodigoxin-bovine serum albumin conjugate formed antibodies which bound a radioiodinated dihydrodigoxin-ribonuclease conjugate. This binding was inhibited by dihydrodigoxin. After affinity chromatography on a digoxin-ribonuclease-Sephacryl immunoadsorbent to remove antibodies which cross-reacted with digoxin, dihydrodigoxin was 300 times more effective than digoxin in inhibiting the binding of tracer by antibody. Digoxin-absorbed antidihydrodigoxin antibodies were coupled to Sephacryl and were used to develop a solid-phase radioimmunoassay capable of detecting 250 to 500 pg of dihydrodigoxin in 1 ml of human serum or urine. This radioimmunoassay has been used to define the pharmacokinetics of the metabolite in four normal human volunteers who ingested 125 to 500 micrograms of dihydrodigoxin by mouth. Dihydrodigoxin was quickly absorbed, with maximal serum concentrations achieved within 45 to 105 min, followed by a rapid fall in serum immunoreactivity over 2 to 4 hr and then by a slower, more gradual decline. The terminal half-life (beta) in serum varied from 4.24 to 11.9 hr (mean +/- S.E. = 8.1 +/- 1.3 hr). Most of the administered dose was excreted in the urine, with cumulative urinary recovery varying inversely with the dose. Urinary half-lives averaged 13.8 +/- 2.1 hr, and renal clearance rates were similar to those of creatinine. Dihydrodigoxin is rapidly absorbed and excreted in man and appears to be eliminated from the body at a faster rate than digoxin.