Petrus J. Laubscher

Prolactin, testosterone and cortisol as possible markers of changes in cardiovascular function associated with urbanization

People living in large informal settlements in South Africa showed a significant increase in cardio/cerebrovascular disease. This study was undertaken to compare the cardiovascular and endocrine parameters of urbanized and rural black female and males. The hormone levels such as prolactin, cortisol and testosterone may also change with urbanization and could make a contribution to the high rate of hypertension. For this study, 1202 black subjects were selected from 37 randomly selected rural and urbanized settlements. Resting blood pressure was recorded with a Finapres apparatus. Cardiac output, stroke volume, heart rate, total peripheral vascular resistance and compliance had been obtained with the Fast Modelflow software program. An acute laboratory stressor (hand dynamometer exercise) was applied to challenge the cardiovascular system and the measurements were repeated. Blood sampling was done and hormone levels were determined by biochemical analyses. For females, significant lower levels of cortisol were found in the urban strata in comparison with the rural strata. The testosterone levels were significantly lower and the prolactin levels significantly higher for females in the informal settlements compared with the rural strata. It is noticeable that most cardiovascular parameters showed the highest changes with the application of the stressor in the informal settlement strata and the lowest in people living on farms for both male and female. The prolactin levels in males are significantly higher in the informal settlement stratum. Subjects living in informal settlements showed a noticeable endocrine pattern of ongoing stress that can be associated with changes in the cardiovascular parameters with urbanization. This can partly explain the reported high rate of cardio/cerbrovascular disease in black South Africans living in informal settlements.

The influence of acculturation on endocrine reactivity during acute stress in urban black males

Urbanization is a world-wide phenomenon and results in a radical and sometimes total change in living conditions. This process is accompanied by a significant increase in the incidence of western-type diseases virtually unknown in traditional rural communities. Especially in a multicultural society like South Africa, rural people moving to the city will experience cultural shock leading in many cases to a large degree of acculturation. In this study the effect of acculturation on endocrine reactivity was studied in a population of Tswanas. It was found that significant differences in endocrine reactivity exist not only between rural Tswanas and urban whites but in some instances also between rural Tswanas and urban Tswanas. During the cold pressor test, the testosterone reactivity and to a lesser extent the prolactin reactivity of the urban Tswanas tended to approach that of the white group as a function of their level of acculturation. All the Tswana groups had a significantly higher plasma renin activity during acute stress than the whites, which could have a bearing on the tendency of urban blacks to develop hypertension.

Cardiovascular reactivity patterns elicited by the cold pressor test as a function of aging

Background and aims: The cold pressor test has been widely used in previous cardiovascular reactivity studies as a predictor of hypertension. However, the influence of the physical adaptations of the arterial wall with increasing age on reactivity has not been delineated. Methods: 64 men divided into 5 different age groups participated in a laboratory protocol consisting of submerging one hand in ice water for one minute while changes in blood pressure were continuously measured. Results: The results indicated that with increasing age, the systolic blood pressure change, especially the rate of change (slope) is more pronounced than changes in diastolic blood pressure. Conclusions: With increasing age, there is a shift from a diastolic blood pressure reactivity pattern to a more systolic blood pressure reactivity pattern during application of the cold pressor test. This could be ascribed to a decrease in arterial compliance.