Effect of propranolol on cyclic AMP excretion and - NCBI

ORIGINAL ARTICLES

Effect of propranolol on cyclic AMP excretion and plasma renin activity in labile essential hypertension Pavel Hamet, m.d., ph.d., Otto Kuchel, m.d.,.sc.d., f.r.c.p.[c], J. L. Jacques Genest, c.c, m.d., f.r.c.p.[c], f.a.c.p., Montreal

Summary: Labile hypertension is

often associated with elevated cardiac output, increased plasma renin activity (PRA) and urinary cyclic AMP excretion in response to upright posture and to isoproterenol. The ^-blocking agent propranolol was demonstrated to be an effective therapeutic agent in this condition. The effect of posture on cyclic AMP, PRA, pu!se rate and blood pressure was therefore studied during the administration of propranolol and a placebo in patients with labile hypertension. With the patient on placebo, upright posture induced an increase in pulse rate, cyclic AMP excretion and PRA. Propranolol administration decreased the recumbent and upright .blood pressures, pulse rate and PRA. Cyclic AMP excretion remained unchanged in the recumbent position but the postural increase was abolished. No appreciable changes in catecholamine excretion occurred during propranolol administration. Propranolol normaiizes some humoral as well as hemodynamic abnormalities of labile hypertension and therefore may be of benefit in long-term treatment and possibly also in the prevention of stable hypertension.

Resume: L'hypertension labile est souvent associee a un debit cardiaque eleve, a une activite de la renine plasmatique augmentee et a une elevation de I'excretion de I'AMP cyclique urinaire en reponse a la position debout et a I'isoproterenol. L'agent £-bloqueur, le propranolol, s'est avere un traitement efficace chez des patients souffrant d'hypertension labile. Pour cette raison, I'effet de la position debout sur I'AMP cyclique urinaire, I'activite de la renine plasmatique, le pouls et la pression arterielle a ete etudie pendant ^administration du propranolol et d'un placebo chez ces patients. Sous I'administration du placebo, la position debout a produit une augmentation du pouls, de I'excretion de I'AMP From the Clinical Research Institute of Montreal and the Hypertensionof Montreal, Hotel-Dieu Hospital. This work was supported through grants MT-2915, MT-3708 and the block grant for hypertension from the Medical Research Council of Canada and by the Quebec Heart Foundation. ?Presented at the 55th Annual Meeting of the U.S. Endocrine Society, Chicago, June 1973. This work represents a part of the work awarded the 1972 Annual Research Award of the Canadian Society of Cardiology. Reprint requests to: Dr. Otto Kuchel, Clinical Research Institute, 110 Pine Ave. West, Montreal 130, Que.

Nephrology Service, University

Cuche,

m.d.,

Roger Boucher, ph.d.

and

cyclique

et de I'activite de la renine plasmatique. L'administration du propranolol a abaisse la pression arterielle en position couch6e et debout ainsi que le pouls et I'activite de la renine plasmatique; I'excretion de I'AMP cyclique n'a pas ete influences dans la position couchee mais I'augmentation posturale a ete empechee. Aucun changement appreciable ne s'est produit dans I'excretion des catecholamines pendant I'administration du propranolol. Le propranolol normadise quelques anomalies de l'hypertension labile tant de nature humorale qu'hernodynamique. Ceci pourrait etre d'un certain profit dans le traitement a long terme de l'hypertension labile et possiblement aussi dans la prevention de l'hypertension stable.

Labile essential hypertension is often associated with in¬ pulse rate, cardiac output and plasma renin activity

creased

(PRA).1^

Several workers have reported morphological, pharmacological and clinical evidence for sympathetic regulation of plasma renin activity.511 This regulatory mechanism acts predominantly through the activation of /3-adrenergic re¬ ceptors.8 Accordingly, /^-blocking agents are able to diminish the PRA.10-1214 A close relation between /?-adrenergic activity and adenylate cyclase has been established.15'16 We reported that urinary cyclic adenosine monophosphate (AMP) excretion increases in response to upright posture and isoproterenol infusion in labile essential hypertension as opposed to a decrease in control subjects.17 The present study was therefore undertaken in order to establish the effect of treatment by a /2-blocking agent (propranolol) on cyclic AMP excretion and PRA, as well as on pulse rate and blood pressure.

Materials and methods with labile essential hypertension (WHO, selected for this study according to the fol¬ lowing criteria: blood pressure elevated over 140/90 mm. Hg on several occasions, but decreasing to below 140/90 during hospitalization; normal on physical examination, in¬ cluding absence of retinopathy; normal levels of serum Na+, K+ and total CO2""; normal renal function and rapid sequence intravenous pyelogram; normal electrocardiogram Seven

stage I)

patients

were

CMA JOURNAL/DECEMBER 1, 1973/VOL. 109 1099

and renal arteriogram; absence of any overt signs of arterioatherosclerosis of large vessels.18 During the 10 days of the study the patients received a standard diet containing 135 mEq. of sodium and 90 mEq. of potassium per day. Smoking and consumption of beverages containing xanthines were forbidden for at least 12 hours prior to urine collection. All subjects adhered to a standard liquid intake of 600 ml. for the six hours before midnight on the evening preceding the test and 125 ml. per hour during the test, including the fluid taken at breakfast; this meal was taken before the beginning of the collection. The experimental design consisted of two periods of five days, during which the subjects received either placebo or the ^-blocking agent propranolol (Inderal®) in alternate periods. The placebo and the propranolol tablets* were identical in colour, size and shape. Propranolol was ad¬ ministered as 40 mg. tablets four times a day. In the last two days of each period the effect of posture was studied. Subjects had been in the recumbent position since the preceding evening. They first voided (urine discarded) at 8:30 a.m. in the recumbent position and then the urine was collected until 12:30. One day the collection was taken with the subject recumbent and at rest, and the other day with the subject up and walking leisurely during the entire four-hour period. Blood pressure and pulse rate were taken every hour during recumbency and while in the upright position. The sequence of administration of the drug or placebo as well as the sequence of position were randomized and conducted in a double-blind fashion. Urine was collected on ice and immediately frozen at -90°C. until determination of cyclic AMP. Blood samples were drawn for PRA measurement at noon at the end of each collection, recumbent or upright.

PLACEBO

PROPRANOLOL

RECUMB. UPRIGHT

RECUMB. UPRIGHT

HEART RATE/min

FIG. 1.Effect of medication on heart rate, mean blood pressure, cyclic AMP excretion and plasma renin

.Propranolol and placebo tablets Ayerst Laboratories, Montreal.

were

Table I.Effect of posture

during placebo administration in labile essential hypertension

kindly supplied by M. D. Dufresne,

activity (PRA) (mean ± S.E.).

PR Mean pulse rate per minute during four hours of study. MBP Mean of blood pressure in mm. Hg (diastolic + Vz of pulse pressure) during the same period. Vol. Volume of urine in ml./min. during the same period. Creat. Creatinine excretion in mg./min. cAMP/min. Cyclic AMP excretion in nM. AMP/Cr Cyclic AMP excretion expressed in jaM and corrected per g. of creatinine. PRA Plasma renin activity in ng./ml./hr. =

=

=

=

=

=

=

Table II.Effect of posture

during propranolol administration in labile essential hypertension

1100 CMA JOURNAL/DECEMBER 1, 1973/VOL. 109

Urinary cyclic AMP was measured by the radioimmuno¬ assay method of Steiner et al.19 The intra-assay coefficient of variation was 8.49%. The inter-assay coefficient of cor¬ relation was significant with the enzymatic method20 (r = 0.71, P < 0.05) and protein binding method21 (r = 0.98, P < 0.01), which were also used in our labo¬ ratory. The antibody and radioactive antigen used were purchased from Collaborative Research, Waltham, Massachusetts. The anti-rabbit IgG was purchased from Miles, Kankakee, Illinois.

The urine samples,

analysed without preliminary purifica-

UPRIGHT- PLACEBO

UPRIGHT- PROPRANOLOL

314 391

diluted 5 to 10 times (with 0.05 M sodium buffer, pH 6.2) in order to ensure values falling within the straight segment of the standard curve. All analyses were performed in quadruplicate, each sample rep¬ resenting a different dilution, usually 1/100, 1/200, 1/250

tion,

were

acetate

original sample. The results calculated using an automatized procedure for transformation of the standard curve into a straight line, as recommended by Rodbard, Bridson and Rayford.22 PRA was determined by the method of Boucher et a/.28 Urinary creatinine was estimated by a modification of the method of Folin as described by Cooper and Biggs.24 Urinary catecholamines (norepinephrine and epinephrine) were determined by the method of Anton and Sayre.25 and 1/500 of 1 ml. of the

were

analysis

Statistical % INCREASE

was used for Analysis of variance by randomized blocks of administration of of effect during posture study excretion of propranolol and placebo on urinary volume, creatinine, pulse rate and blood pressure, each patient being considered as a block. The cyclic AMP excretion, having a linear correlation with the creatinine excretion,26 was anal¬ ysed by covariance analysis using the method of reduced Y.27 Since there is no definite evidence that hypertensive pa¬ tients and control subjects belong to the same population,28 the data of cyclic AMP excretion and PRA were, in addi¬ tion, analysed by the nonparametric statistical test of Wilcoxon for paired differences.29-30 The effect of placebo and propranolol as well as that of posture on PRA was submitted to factorial analysis 2 x 2 on logarithms of the original data.

the

*

*

% DECREASE

*

OF URINARY CYCLIC AMP EXCRETION COMPARED TO RECUMBENT VALUES.

FIG. 2.Percentage of change of cyclic AMP excretion during upright position from values observed in recumbent position in the same patients receiving either placebo or propranolol.

Statistical analysis of the effect of posture Table Illa labile essential hypertension MBP* Pulse* 0.3 16.58 Placebo NS