Adenohypophyseal function in bitches treated with medroxyprogesterone acetate

Abstract

The aim of this study was to investigate the effects of treatment with medroxyprogesterone acetate (MPA) on canine adenohypophyseal function. Five Beagle bitches were treated with MPA (10 mg/kg, every 4 weeks) and their adenohypophyseal function was assessed in a combined adenohypophyseal function test. Four hypophysiotropic hormones (CRH, GHRH, GnRH, and TRH) were administered before and 2, 5, 8, and 11 months after the start of MPA treatment, and blood samples for determination of the plasma concentrations of ACTH, cortisol, GH, IGF-1, LH, FSH, prolactin, ␣-MSH, and TSH were collected at −15, 0, 5, 10, 20, 30, and 45 min after suprapituitary stimulation.MPA successfully prevented the occurrence of estrus, ovulation, and a subsequent luteal phase. MPA treatment did not affect basal and GnRH-induced plasma LH concentrations. The basal plasma FSH concentration was significantly higher at 2 months after the start of MPA treatment than before or at 5, 8, and 11 months after the start of treatment. The maximal FSH increment and the AUC for N.J. Beijerink et al. / Domestic Animal Endocrinology xxx (2006) xxx-xxxmonths of MPA treatment. Differences in mean basal plasma GH concentrations before and during treatment were not significant, but MPA treatment resulted in significantly elevated basal plasma IGF-1 concentrations at 8 and 11 months. MPA treatment did not affect basal and stimulated plasma ACTH concentrations, with the exception of a decreased AUC for ACTH at 11 months. In contrast, the maximal cortisol increment and the AUC for cortisol after suprapituitary stimulation were significantly lower during MPA treatment than prior to treatment. MPA treatment did not affect basal plasma concentrations of prolactin, TSH, and ␣-MSH, with the exception of slightly increased basal plasma TSH concentrations at 8 months of treatment. MPA treatment did not affect TRH-induced plasma concentrations of prolactin and TSH.In conclusion, the effects of chronic MPA treatment on adenohypophyseal function included increased FSH secretion, unaffected LH secretion, activation of the mammary GH-induced IGF-I secretion, slightly activated TSH secretion, suppression of the hypothalamic-pituitary-adrenocortical axis, and unaffected secretion of prolactin and ␣-MSH.

Diabetes Mellitus in Elkhounds Is Associated with Diestrus and Pregnancy

“…Normal cycling nonpregnant female dogs have an altered profile of blood concentrations of GH during the luteal phase of the estrus cycle with less pulsatility and higher basal secretion due to mammary secretion of GH 28 and that GH and insulin concentrations are higher in older compared with younger dogs after injection of progestins 29 . In the present study, both cases and controls had higher concentrations of GH and IGF‐1 than did anestrus dogs in a recent study by Beijerink et al using the same assays 9 . However, the differences in GH concentrations between cases and controls in the present study were nominally much smaller than in an earlier study by Eigenmann et al on diestrus diabetes in which all diabetic dogs were clearly acromegalic 3 .…”

“…c C-peptide was measured with a commercially available radioimmunoassay for canine C-peptide. d The instructions given for the kit were followed accurately, except that the protease inhib-itor aprotinin e was added just before analysis instead of immediately after sampling as earlier described by Fall et al 8 GH was analyzed with a commercially available RIA for porcine and canine GH f as described earlier by Beijerink et al 9 Serum IGF-1 concentrations were measured by an in-house RIA, originally designed for use on human sera, after acid-ethanol extraction to remove interfering IGF binding proteins as described in detail by Favier et al 10 In Vitro Transcription and Translation of GAD65 and Immunoprecipitation. A pCMV6 entry plasmid carrying a T7 promoter sequence and GAD2, 11 the gene encoding canine GAD65, was designed and purchased from Origene.…”

Plasma ACTH, α-MSH and cortisol variations in the dog during the oestrous cycle in different photoperiods

“…In dogs, Beijerink et al (2007) did not find changes in ACTH plasma concentrations in bitches treated with medroxiprogesterone, but found a lower response to CRF stimulation after the drug had been administered for a long time. The differences with this study could be explained by a differential effect between synthetic and native P 4 (related to chemical structure or physiological concentrations vs. therapeutic doses).…”

“…Although it has been found that both in women and sheep in advanced pregnancy, plasma ACTH and cortisol are increased, the effect of P 4 on the previously mentioned hormones could not be determined (Goland et al 1994;Keller-Wood 1998;Keller-Wood and Wood 2001). Moreover, there were no variations in ACTH and alfa-melanocyte-stimulating hormone [α-MSH] concentrations in bitches that were treated with synthetic P 4 (Beijerink et al 2007).…”

Quantification of collagen fibers in canine uteri treated with medroxyprogesterone acetate

“…Another effect of MPA is said to be the increase in the baseline concentration of gonadotropins, particularly in the pulses of adenohypophyseal pulsatile LH from the main endocrine promoter of the ovarian P 4 synthesis (Beijerink et al 2008). Moreover, it has been reported that MPA induces the secretion of insulin-like growth factor (IGF-I; Beijerink et al 2007), which has been shown to be a powerful stimulator of protein synthesis and collagen gene expression (Gillery et al 1992).…”