THE EFFECTS OF TESTOSTERONE AND OF TESTOSTERONE PROPIONATE ON RENAL FUNCTIONS IN MAN

Gender differences in hypertension and kidney disease

Gender differences exist in hypertension, the prevalence of several renal diseases, progression of established renal disease, and within the ESRD program, including renal transplantation. Sex hormones play key roles in the pathogenesis and outcome of disease processes. Observational data suggest gender differences in the prevalence and outcome of several renal diseases. The molecular mechanisms associated with physiologic phenomena needed to explain gender differences in renal disorders, however, remain largely obscure. The interaction of psychosocial, economic, medical, and genetic differences associated with discrepancies between the genders in the process of receiving a renal transplant and sustaining graft function are currently unclear. Additional studies are needed in these and other areas to explain gender differences in the incidence, prevalence, and outcome of renal disease.

The role of gender in the progression of renal disease

The rate of progression of certain renal diseases in animals is greater in men than in women. In various animal models of renal disease, investigators have concluded that the presence of testosterone explains the worse course in men compared with women, whereas in other diseases, estrogen seems to confer protection for women. The gender disparity in renal disease progression found in animals is seen in certain human renal diseases, including chronic renal disease, membranous nephropathy, immunoglobin A nephropathy, and polycystic kidney disease. In humans, the differences between the genders in renal disease progression cannot be fully explained by differences in blood pressure or serum cholesterol levels. The underlying mechanisms for this gender disparity are potentially related to differences between the sexes in glomerular structure, glomerular hemodynamics, diet, variations in the production and activity of local cytokines and hormones, and/or the direct effect of sex hormones on kidney cells. Further investigation into the contribution of gender to renal disease progression may aid us in developing strategies for slowing this pathological process.

Role of androgens in mediating hypertension and renal injury

1. Men are generally at greater risk for cardiovascular disease than are women, particularly with regard to enhanced progression of hypertension and loss of renal function. Despite these gender differences in the progression of hypertension and renal disease in humans and animals, the mechanisms responsible are unknown. 2. Castration in males has been shown to slow the progression of hypertension and ameliorate the loss in renal function. When serum testosterone was measured in the developing male spontaneously hypertensive rat (SHR), the peak serum testosterone level at 12 weeks coincided with the time when differences in systolic blood pressure could be measured between intact male SHR and females or castrated male SHR. Ovariectomy does not affect blood pressure in female SHR but testosterone treatment of ovariectomized females for 5 weeks results in exacerbation of hypertension almost to the level found in intact male SHR. These data strongly suggest a role for androgens in mediating the gender differences in hypertension. 3. The mechanisms by which androgens could increase blood pressure are not known. We have recently shown that, at comparable renal perfusion pressures, there is a hypertensive shift in the pressure-natriuresis relationship in male SHR compared with females or castrated male SHR. Testosterone treatment of ovariectomized female SHR also causes a rightward shift in the pressure-natriuresis relationship. 4. We hypothesize that androgens increase arterial pressure by causing a hypertensive shift in the pressure-natriuresis relationship, either by having a direct effect to increase proximal tubular reabsorption or by activation of the renin-angiotensin system. We also hypothesize that the enhanced proximal tubular reabsorption leads to a tubuloglomerular feedback-mediated afferent vasodilation, which, in combination with the increase in arterial pressure, results in glomerular hypertension and renal injury.

The impact of gender on the progression of chronic renal disease

Observations in experimental animals and in humans have shown that the rate of progression of renal disease is influenced by gender. Deterioration of renal function in patients with chronic renal disease is more rapid in men than in women, independent of differences in blood pressure or serum cholesterol levels. In addition to genetically determined differences between the sexes in renal structure and function, sex hormones may directly influence many of the processes implicated in the pathogenesis of renal disease progression. Potential mechanisms include receptor-mediated effects of sex hormones on glomerular hemodynamics and mesangial cell proliferation and matrix accumulation as well as effects on the synthesis and release of cytokines, vasoactive agents, and growth factors. In addition, estrogens may exert potent antioxidant actions in the mesangial microenvironment, which may contribute to the protective effect of female gender.