UNIVERSITY OF THE WITWATERSRAND MEDICAL SCHOOL, 7 YORK ROAD, PARKTOWN, JOHANNESBURG. 2193, SOUTH AFRICA. RECEIVED FOR ...
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Relationship Between Plasma Insulin and Blood Pressure in South African Black Women in Johannesburg BARRY I. JOFFE, DSC VANESSA R. PANZ, FSLMT JEFFREY R. WING, FCP FREDERICK J. RAAL, FCP HAROLD C. SEFTEL, DIP MED
OBJECTIVE— To examine the relationship between fasting plasma insulin and blood pressure (BP) in 40 urbanized normotensive South African black women aged 24-60 yr, and to assess the effects of body mass index (BMI) and fasting plasma glucose on BP. RESEARCH DESIGN A N P METHODS — The women comprised equal numbers of young nonobese nondiaberic subjects, middle-aged nonobese nondiabetic subjects, middle-aged obese nondiabetic subjects, and middle-aged obese newly diagnosed noninsulin-dependent diabetic subjects. Systolic and diastolic BPs were recorded (in duplicate) after 15 min of recumbency, and fasting plasma glucose and insulin levels were determined thereafter. The data were analyzed by simple and multivariate regression. RESULTS— There was a wide distribution of individual physical and biochemical features. With simple correlations, systolic BP correlated significantly with age, BMI, and fasting glucose but not with insulin. Diastolic BP correlated significantly with all four variables (r = 0.37, P < 0.05). When adjusted for age, BMI, and glucose, however, the significant correlation between diastolic BP and insulin diminished (r = -0.04). CONCLUSIONS— As in other nonwhite communities, plasma insulin does not appear to play a major role in regulating the BP of South African black women.
T
he link between hyperinsulinemia and hypertension is the subject of much controversy (1-3). Reasons
for the postulated relationship are unclear but might involve renal sodium retention (4), sympathetic nervous system
FROM THE CARBOHYDRATE AND LIPID METABOLISM RESEARCH GROUP; AND THE DIVISION OF ENDOCRINOLOGY, DEPARTMENT OF MEDICINE, UNIVERSITY OF WITWATERSRAND MEDICAL SCHOOL, JOHANNESBURG, SOUTH AFRICA. ADDRESS CORRESPONDENCE AND REPRINT REQUESTS TO R. I. JAFFE, DSC, DEPARTMENT OF MEDICINE, UNIVERSITY OF THE WITWATERSRAND MEDICAL SCHOOL, 7 YORK ROAD, PARKTOWN, JOHANNESBURG 2193,
SOUTH AFRICA.
RECEIVED FOR PUBLICATION 20 FEBRUARY 1991
556
AND ACCEPTED IN REVISED FORM 2 OCTOBER
1991.
activation (5), or vascular smooth muscle cell hypertrophy (6) induced by increased concentrations of insulin. If this hypothesis is valid, we would anticipate blood pressure (BP) to be highly positively correlated with plasma insulin levels over a wide range of measurements, especially in communities predisposed to the development of hypertension. One such population is the South African urban black community in which the prevalence of essential hypertension is extremely high (7). No study of the relationship between BP and circulating insulin levels in this population has been reported. Therefore, during an investigation of the insulin-receptor status of urbanized black women with different degrees of obesity and glucose intolerance, we took the opportunity of examining this controversial issue.
RESEARCH DESIGN AND METHODS — Forty ambulant urbanized normotensive (screening BP < 160/95 mmHg) black women were studied. They comprised 10 young (age 24—36 yr) nonobese (body mass index [BMI] 19.3-24.9 kg/m2) nondiabetic women, 10 middle-aged ( 4 0 - 6 0 yr old) nonobese nondiabetic subjects, 10 middle-aged obese (BMI >30.0 kg/m2) nondiabetic subjects, and 10 middle-aged obese newly diagnosed but untreated patients with non-insulin-dependent diabetes mellitus (fasting blood glucose 8-16 mM). Normal glucose tolerance was established by preliminary glucose tolerance testing (75-g oral glucose administration). The 30 nondiabetic women were randomly selected from the domestic work force at the University of the Witwatersrand Medical School, and the diabetic patients were 10 consecutive newly presenting patients at the polyclinic of Hillbrow Hospital. None of the women smoked or were taking any medication known to affect BP or carbohydrate metabolism. They all gave informed consent to participate in the study, which was approved by the ethics
DIABETES CARE, VOLUME 15, NUMBER 4, APRIL 1992
Short report
Table 1—Simple and partial correlation coefficients (r) between blood pressure (BP) and other variables in total study population INDEPENDENT VARIABLES (R)
VARIABLE
DEPENDENT
BP
ADJUSTED
FASTING PLASMA
FASTING
INDEX
GLUCOSE
PLASMA INSULIN
0.33* 0.40*
0.48t 0.631=
0.32* 0.30*
NONE; SIMPLE CORRELATION
SYSTOLIC DIASTOLIC
BP
BODY MASS AGE
AGE AND BODY MASS INDEX
0.05 -0.14
SYSTOLIC DIASTOLIC
BP
0.20 0.37 -0.18 -0.08
AGE, BODY MASS INDEX, AND FASTING PLASMA GLUCOSE
-0.18 -0.04
SYSTOLIC DIASTOLIC
*P < 0.05. t P < 0.01. *P < 0.001.
committee for research of human subjects at our institution. Definitive tests were performed after a 10-h overnight fast, with menstruating females being studied in the follicular phase of the menstrual cycle (subsequently confirmed by plasma progesterone measurements 36 nM [
