Renal function, plasma sodium and osmolality during the menstrual cycle

In order to assess whether hormonal changes occurring during the menstrual cycle affect function, glomerular filtration rate (C cr), and proximal tubular reabsorption of sodium and water (lithium clearance; C li) were assessed in 9 healthy women in 2 phases of the menstrual cycle. Plasmar sodium and osmolality were also measured. Each subject was studied three time ("basal", "proliferative" and "luteal" phases), point on her customary sodium intake, and in a controlled (sitting) posture. There were no significance differences between the phases with respect to any of the renal variables studied. There was a significantly lower plasma sodium in the luteal phase, and a trend towards lower plasma osmolality.

Renal lithium clearance in essential hypertension

There is considerable interest in whether a defect in renal sodium handling is important in the development of essential hypertension. A recent report indicated that the proximal tubule might be involved, since fractional lithium clearance, a measure of the fraction of filtered sodium reaching the end of the proximal tubale, was reduced in hypertentive patients. However, ther were a number of objectionable points in that paper. In the present study, we measured clearances of creatinine (C cr), lithium, (C li) and sodium (C na) in 21 hypertensive patients and 21 controls matched for age, sex and ethnic background. Clearances were measured over a 4-h period during which the subject were seated. The result provide no evidence for altered proximal tubular sodium handling in essential hypertension under the conditions of the study.