EFFECT OF BLOOD-SAMPLING AND ADMINISTRATION OF ACTH ON CORTISOL AND PROGESTERONE LEVELS IN OVARIECTOMIZED ZEBU COWS (BOS-INDICUS)

Four zebu cows were bilaterally ovariectomized through lateral laparot omy. Three months after ovariectomy, blood samples were collected by j ugular venipuncture daily for 5 consecutive days prior to a single inj ection of ACTH to establish baseline concentrations of cortisol and pr ogesterone. Baseline concentrations of cortisol and progesterone were 31 +/- 5 nmol/L and 0.3 +/- 0.01 nmol/L, respectively. On the day of A CTH treatment the cows were allowed to rest for 2 h to reduce the stre ss of cannulation before the sampling period started. Blood samples we re collected every 30 min from 2 h before until 2 h after the injectio n of 6 mu g ACTH and hourly between 2-6 h after ACTH injection. A sign ificant increase was observed in cortisol secretion from 90 min before until 120 min after ACTH injection. No significant increase was obser ved in progesterone secretion before ACTH injection. After ACTH inject ion progesterone was significantly elevated for 120 min. Four weeks af ter the ACTH treatment the cows were cannulated again and blood sample s were collected following the same bleeding schedule used during the ACTH experiment. Instead of ACTH a saline injection was given via the catheter. A significant increase in cortisol concentration was recorde d 90 min before saline injection. This increase was not accompanied by an elevation in progesterone concentration. No significant changes we re observed in cortisol and progesterone levels after saline injection . When cortisol was added to a plasma pool having a progesterone conce ntration of 0.3 nmol/L and a cortisol concentration of 25.4 nmol/L and assayed for progesterone in 2 different assays no increase in progest erone concentration was observed. We conclude that the adrenal glands can be an extra-ovarian source of progesterone during stress in Zebu c ows.