Progesterone and the distribution of pituitary gonadotropin isoforms in cattle

Abstract

The objective of the present study was to determine the relative proportion of gonadotropin isoforms in bovine pituitary glands affected by progesterone. Twelve postpubertal heifers (Swiss-Zebu) were assigned to three groups ( n = 4): intact animals in the luteal phase of the estrous cycle (diestrus group); ovariectomized heifers with (OVXP) or without progesterone treatment (OVX). Prior to pituitary gland collection, a blood sample was taken from each animal to determine the circulating progesterone concentration. Pituitary protein extractions processed by chromatofocusing were eluted with a pH gradient ranging from 10.5 to 3.5. The LH and FSH eluent was grouped on the basis of the following three criteria: (1) as either a basic (pH ≥7.5), neutral (pH 7.4–6.5) and acid (pH ≤6.4); (2) according to the pH unit (pH ≥10.5–3.5); (3) on the basis of distinct isoforms 12 peaks of which (A–L) were identified for LH and 11 (I–XI) for FSH. The analysis by range of pH and by pH of elution in the OVX and OVXP groups showed no difference in the LH and FSH isoform ratio, but diestrus cattle differs having a greater ratio ( p < 0.05) of basic LH isoforms (87.5 ± 0.4%) and lesser ratio ( p < 0.05) of acid isoforms (5.4 ± 0.7%). In the diestrus group, the ratio of acid FSH isoform increased (62.1 ± 1.7%), while neutral isoforms decreased (5.7 ± 0.4%, P < 0.05). The analysis by isoform type of LH revealed a greater proportion of isoforms C (pH 9.4) and E (pH 9.0) in the groups with circulating progesterone when compared to the OVX group. The heterogeneity of FSH was quantitatively similar in most isoforms in the three groups, with the exception of the predominant isoform (VIII, pH 4.9) that was more abundant in the diestrus group ( p < 0.05). These results indicate that progesterone with other gonad factors influence the pituitary glicosylation altering the relative proportions of gonadotropin isoforms.