Androstenedione and the Control of Luteinizing Hormone in the Ewe During Anoestrus

Abstract

Androstenedione and oestradiol were measured by radioimmunoassay in the utero-ovarian venous plasma of two ewes during anoestrus. The concentrations of both steroids were significantly higher than the corresponding concentrations in peripheral plasma, indicating that androstenedione and oestradiol are secreted by the ovary during anoestrus. The concentration of LH during anoestrus was measured by radioimmunoassay in jugular venous plasma of control ewes, ewes immunized against 11alpha-OH-androstenedione-bovine serum albumin and ewes that had been ovariectomized and hystrectomized 9 months previously. During a 12 h sampling period, discharges of LH occurred more frequently in the immunized ewes than in the control group but less frequently than in the ovariectomized group. The frequency of discharge was positively correlated with the titre of androstenedione antibodies in the immunized animals. After injection of 25 mug oestradiol benzoate (OB) all controls, 3 out of 5 immunized and 4 out of 5 ovariectomized-hysterectomized ewes showed positive feedback. No positive feedback occurred in the two ewes with the highest antibody titres to androstenedione, but negative feedback in response of OB apperaed to function normally in all the androstenedione immunized sheep. It is postulated that androstenedione, or one of its metabolites, normally modulates the effects of oestradiol in the control of gonadotrophin secretion in the ewe.

Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

“…The mean secretion of each group was compared to that of controls by Student's t-test. For analysis of LH secretion by the pituitary gland, it has been accepted that pulsatile secretory episodes are reflected in transitory elevations of the hormone levels in plasma (Lincoln 1976;Martensz et al 1976). In the present study, a secretory episode was identified when a sample value exceeded the level of the previous sample by at least two standard deviations of the assay value of the previous sample.…”

Reproductive effects of immunizing heifers against androstenedione and oestradiol-17

“…of animals indicated in (Scaramuzzi et ai, 1977 ;Van Look et ai, 1978;Scaramuzzi et ai, 1980a). Immunization against androstenedione increases the frequency of luteinizing hormone (LH) discharges and mean levels of LH in ewes (Martensz, Baird, Scaramuzzi & Van Look, 1976) in conjunction with increasing the number of follicles > 3 mm in diameter and ovulation rate (Scaramuzzi et ai, 1980a). A lack of significant differences in peripheral androstenedione or oestrogen concentrations between immunized (Groups III and IV) and control (Groups I and II) heifers in this study may be related to the relatively low titres (1:100 and 1:1000) acquired in the short immunization period (< 150 days).…”

Differential effects of LH-RH immunoneutralization on LH and FSH secretion in the ewe

“…The concentration of LH was determined by radioimmunoassay (Martensz, Baird, Scaramuzzi & Van Look, 1976) of duplicate quantities of plasma and results were expressed in terms of ng NIH-LH-S14/ml. The sensitivity of the assay was 0-3 ng/ml and the intra-and inter-assay coefficients of variation were 8 and 10% respectively.…”