Electrolyte Metabolism During the Oestrous Cycle in the Rat

Abstract

In the present study renal electrolyte function and
adrenal cortical activity were determined during the rat
oestrous cycle, and in ovariectomised animals given
oestradiol and progesterone therapy.

Initial studies showed a variation in the sodium content
of uterus; kidney, liver, plasma. heart and skeletal muscle
during the oestrous cycle, with higher levels of sodium at
oestrus than at dioestrus. The water and potassium content
of the tissues examined showed a less marked variation
during oestrous cycle.

The variation in tissue electrolytes during the oestrous
cycle was paralleled by a variation in renal electrolyte
function. Urine flow, urinary sodium concentration and
excretion rate were significantly lower at oestrus, when
ovarian hormones are raised, than at dioestrus. Urinary
potassium concentration and excretion rates were significantly
higher at oestrus than at dioestrus. No significant
variation in glomerular filtration rate was observed during
the oestrous cycle.

Spironolactone blocked the increased sodium and water
retention and potassium excretion observed at oestrus,
but had little effect on renal electrolyte function in
dioestrous or ovariectomised animals. Spironolactone has
been shown to inhibit the action of mineralocorticoids on
the distal tubules of the kidney. This, therefore,
suggested that the adrenal cortex was involved in the
variation in renal electrolyte function observed during the oestrous cycle, with an increase in adrenal activity at oestrus when ovarian hormones are also raised.

In order to investigate further the role of ovarian
hormones in the observed variation in renal electrolyte
function during the oestrous cycle, oestradiol and progesterone
were administered to ovariectomised rats.

Prolonged administration of oestradiol, progesterone and
oestradiol + progesterone all significantly reduced urine
flow, urinary sodium concentration and excretion rate and
increased potassium excretion, but had no effect on glomerular
filtration rate in ovariectomised animals. Spironolactone
administration blocked the action of ovarian hormone
administration on renal electrolyte function, again
implicating adrenal cortical action. A single, physiological
dose of oestradiol resulted in a progressive increase in
sodium and water retention and potassium excretion 5 to 8
hours after hormone administration. Spironolactone was
found to block the action of oestradiol on renal function.

Twelve hours after oestradiol administration renal
electrolyte function was not significantly different to that
observed in control ovariectomised animals.

In contrast to the effect of oestradiol administration
on renal electrolyte function, it was found that administration
of physiological doses of progesterone had little effect on
renal electrolyte function compared with control ovariectomised
rats. The evidence obtained from investigation of renal
electrolyte function during the oestrous cycle suggested a
variation in adrenal activity at this time. A significant variation in aldosterone and corticosterone secretion rates were found during the rat oestrous cycle, the highest secretion rates being observed at pro-oestrus when oestrogen
levels were also raised.

It is suggested, therefore, that the action of ovarian
hormones on renal electrolyte function is a result of an
initial stimulation of the adrenal cortex by the ovarian
hormones, primarily oestrogens.

Date of Award	Mar 1972
Original language	English