Date of Award

1983

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

A study of the basic mechanism of aldosterone secretion was performed on 15 month old Holstein heifers. Animals were fitted with indwelling jugular catheters and estrous cycle was synchronized with PGF(,2(alpha)). Effects of adrenocorticotrophic hormone (ACTH) and angiotensin II (AII) on the secretion of aldosterone, cortisol, progesterone and other parameters such as sodium and potassium that influenced aldosterone secretion were analyzed by Latin Square design, replicated twice. Treatments consisted of intravenous injections of 200 I.U. ACTH/animal, 18 mg AII/animal, or physiological saline. Blood samples were collected before treatment (0 min), at fifteen and thirty minutes after treatment, and at hourly intervals for six hours, thereafter. Collection was done every other day within each square with three days rest after the first replicate. ACTH and AII resulted in a highly significant (P < .0005) increase in both aldosterone and cortisol. Mean aldosterone values (+OR-) S.E. resulting from ACTH, AII and control treatments were 234.9 (+OR-) 51.7, 466.2 (+OR-) 53.6 and 57.1 (+OR-) 51.9 pg/ml, respectively. Mean cortisol values (+OR-) S.E. resulting from ACTH, AII and control treatments were 29.9 (+OR-) 1.0, 16.2 (+OR-) 1.0 and 5.6 (+OR-) 1.0 ng/ml, respectively. Indications were that the effective stimulators of aldosterone and cortisol were AII and ACTH, respectively. Progesterone was not significantly increased by treatment. Mean values obtained for control, ACTH and AII were 1.0 (+OR-) 0.1, 1.1 (+OR-) 0.1 and 1.2 (+OR-) 0.1 ng/ml, respectively. There were no significant effects of treatment on serum levels of sodium or potassium in the serum of the dairy animals. Twelve pregnant (120-150 days of gestation) Holstein heifers were used to study the circadian rhythm of cortisol, aldosterone, progesterone, sodium and potassium in the dairy cattle during summer in Louisiana. Cortisol was not significantly influenced by time (time 1 = 0600). Aldosterone, sodium, potassium and progesterone changed significantly (P < .01) with time. Aldosterone peaked (116.5 (+OR-) 17.2 pg/ml) at 0800 and then declined at 1600 (26.7 (+OR-) 2.0 pg/ml). Sodium generally increased from 0600 (320.1 (+OR-) 7.3 mg%) to 1800 (377.9 (+OR-) 6.1 mg%), and then declined. Potassium increased from 0600 (20.9 (+OR-) 0.5 mg%) to 2200 (23.0 (+OR-) 0.3 mg%). Progesterone increased from 0700 (2.8 (+OR-) 0.4 mg/ml) to 2400 (7.5 (+OR-) 1.4 ng/ml). Aldosterone was significantly related to temperature associated with the time of the day samples were taken (r = 0.66, P < .02).

Pages

105

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