Posttranslational processing of progonadotropin-releasing hormone (proGnRH) in ewes.

Gonadotropin-releasing hormone (GnRH) is released from hypothalamic neurons into the hypophyseal-portal blood system following enzymatic cleavage of the decapeptide from a large precursor (proGnRH) molecule. The purpose of this study was to determine whether the ability of GnRH-producing neurons to synthesize and/or process proGnRH differed during physiological states associated with a suppressed and enhanced release of GnRH in ewes. Tissues were collected from ovariectomized ewes (OVX, n = 4), OVX-estradiol treated ewes (OVX-E, n = 5), and ewes (n = 7) slaughtered 5 d after parturition (PP). Following euthanasia and exsanguination, stalk-median eminence (SME), medial-basal hypothalamus (MBH) and preoptic areas (POA) were collected. Concentrations of GnRH and proGnRH were determined by radioimmunoassay using specific antisera. Concentrations of GnRH in the SME did not differ (P > .05) between OVX-E and OVX ewes, but both groups contained less (P < .05) GnRH than the SME from PP ewes (4.4 +/- 0.7, 12.1 +/- 3.8 vs 24.3 +/- 5.1 fmol/mg tissue, respectively). Concentrations of proGnRH in SME mimicked those of GnRH and were less (P < .05) in OVX-E ewes than PP ewes, but were not different (P > .05) from those in OVX ewes (.34 +/- .34 vs 3.76 +/- 1.53 and 1.7 +/- .78 fmol/mg, respectively). In the MBH, OVX-E ewes had greater (P < .05) concentrations of GnRH than PP ewes (0.76 +/- 0.29 vs 0.24 +/- 0.04 fmol/mg) and OVX ewes were intermediate (0.41 +/- 0.13 fmol/mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary energy, body condition and calf removal on pituitary gonadotropins, gonadotropin-releasing hormone (GnRH) and hypothalamic opioids in beef cows.

Beef cows (n = 64) were slaughtered to evaluate effects of dietary energy and calf removal (CR) on hypothalamic and adenohypophysial endocrine characteristics. From d 190 of gestation until parturition, cows received maintenance (ME; n = 32) or low (LE; n = 32) energy diets (ME = 100%, LE = 70% NRC recommendations). After parturition, half (n = 16) of each prepartum diet group received low (LE; n = 32) or high (HE = 130% NRC; n = 32) energy diets. At 30 d postpartum, cows were slaughtered 0 or 48 hr after CR. Hypothalami [preoptic area (POA), hypothalamus (HYP), stalk-median eminence (SME)] and pituitaries were collected. Basal and K(+)-induced release of GnRH from SME, and pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) did not differ among groups (P greater than .05). Hypophyseal LH was correlated (P less than .01) with body condition score (BCS) at parturition and slaughter (r = .36 and .47, respectively). Prepartum LE diet increased (P less than .05) met-enkephalin in POA compared to prepartum ME (.59 +/- .05 vs. .44 +/- .04 pmol/mg) regardless of postpartum diet or suckling status. Concentrations of beta-endorphin in combined HYP + POA were decreased (P less than .05) by 48 hr CR (15.1 +/- 1.1 vs. 18.1 +/- 0.7 fmol/mg).(ABSTRACT TRUNCATED AT 250 WORDS)