Age-dependency and dietary influence on the hypothalamic ouabain-like factor in Milan hypertensive rats.
OBJECTIVE
Previous studies have demonstrated that the hypothalamus of the adult Milan hypertensive rat strain (MHS) contains a higher proportion of ouabain-like factor than Milan normotensive (MNS) controls. The present study was designed to demonstrate that the rat standard diet contains a ouabain-like factor similar to that extracted from rat tissue and to investigate the influence of low or high dietary ouabain-like factor content on tissue ouabain-like factor levels at different ages in MHS and MNS rats.


METHODS
MHS and MNS rats were reared on two controlled batches of standard rat diet containing low (batch A 0.09 mu g/kg) and high (batch B 0.7 mu g/kg) concentrations of ouabain-like factor. The mothers of these rats had also been fed with the diet throughout pregnancy and lactation. The hypothalamic content of ouabain-like factor was measured in both strains at 21, 30 and 90 days of age by high performance liquid chromatography fractionation.


RESULTS
(1) The dietary ouabain-like factor content did not influence either the hypothalamic ouabain-like factor yield or systolic blood pressure, either in MHS or MNS rats. (2) As a function of age, the hypothalamic ouabain-like factor content was constant between 21 and 30 days of age in MHS rats, and then decreased by 60% at 90 days. In MNS rats, ouabain-like factor was decreased by 80 and 90%, respectively, at 30 and 90 days, compared to the age of 21 days. (3) At the age of 21 days, MHS rats had 30% lower levels of ouabain-like factor than MNS rats, but 60% higher levels at 30 and 90 days.


CONCLUSIONS
Hypothalamic ouabain-like factor and systolic blood pressure are not influenced by dietary ouabain-like factor, thus excluding a process of passive tissue accumulation. Different mechanisms regulate the age-dependent endogenous ouabain-like factor production and accumulation in MHS and MNS rats, suggesting that the maintenance of higher ouabain-like factor levels in MHS than in MNS at the age of 30 and 90 days contributes to the development and maintenance of hypertension in this strain.
Ferrandi
M
M
Prassis-Sigma Tau Research Institute, Milan University, S. Raffaele Hospital, Italy.
Minotti
E
E
Florio
M
M
Bianchi
G
G
Ferrari
P
P
D000367:Age Factors; D000818:Animals; D001685:Biological Factors / Q000378:metabolism*; D001794:Blood Pressure; D002298:Cardenolides; D004032:Diet; D004077:Digoxin; D006973:Hypertension / Q000378:metabolism* / Q000503:physiopathology; D007031:Hypothalamus / Q000378:metabolism*; D051381:Rats; D012503:Saponins
D001685:Biological Factors; D002298:Cardenolides; D012503:Saponins; C034504:digoxin-like factors; D004077:Digoxin