EFFECTS OF ACUTE CAFFEINE INGESTION AND MENOPAUSE ON SULFATE HOMEOSTASIS IN WOMEN

Inorganic sulfate is a physiological anion which is utilized in the me tabolism of both endogenous compounds and xenobiotics. Its homeostasis is maintained predominantly by facilitated reabsorptive processes in the kidneys. The objectives of the present investigation were to evalu ate the effects of menopausal status and caffeine ingestion on the ser um concentrations and clearance of inorganic sulfate. Thirty-nine wome n who were classified as premenopausal, postmenopausal with or without estrogen treatment, and postmenopausal with osteoporosis participated in the study. The women were studied on two separate occasions follow ing the ingestion of a decaffeinated beverage to which 6 mg caffeine/k g lean body mass or no caffeine was added. All women were habitual caf feine users (mean ingestion of 588 mg caffeine per day) but abstained from all caffeine sources for 2 weeks prior to the control study day. Postmenopausal women with estrogen supplementation exhibited significa ntly lower sulfate serum concentrations (0.24 +/- 0.02 mM vs. 0.32 +/- 0.04 mM in premenopausal women, mean +/- SD, p<0.05) and a decreased renal reabsorption of sulfate for the control (no caffeine) period. Th ere was no difference in serum sulfate or sulfate reabsorption in estr ogen supplemented postmenopausal women, compared with women not taking estrogen. Postmenopausal women with osteoporosis had significantly lo wer creatinine and sulfate clearances than postmenopausal women with e strogen supplementation which may be related to their older age, or fa ctors related to the disease process. The 6 mg/kg dose of caffeine cau sed a diuresis, but no change in GFR, as indicated by urine volume and creatinine clearance values, respectively. Caffeine administration re sulted in an increase in the sulfate excretion rate; there was no chan ge in sulfate serum concentrations. The results of this investigation indicate that menopause results in decreased sulfate serum concentrati ons that may be the consequence of a decreased renal reabsorption of s ulfate. Secondly, this investigation demonstrated that caffeine ingest ion increases the urinary excretion of sulfate, an effect that may be related to the diuretic effect of caffeine or due to a caffeine-induce d alteration in the renal reabsorption of sulfate.