Factors Affecting the Ovarian Response to a Combined Estradiol-Sulpiride Treatment in Seasonally Anovulatory Mares

Sucrose acetate isobutyrate (SAIB) as a delivery vehicle for estradiol and sulpiride: Evaluation of endocrine responses in geldings and ovarian response in seasonally anovulatory mares

Sulpiride in vegetable shortening (VS) stimulates prolactin in horses for up to 10 days. Although effective, a pharmaceutical grade vehicle is needed for clinical application of sulpiride in horses. Sucrose acetate isobutyrate (SAIB), a hydrophobic polymer, may be an alternative to VS. Four in vivo experiments assessed the efficacy of SAIB for delivery of sulpiride, estradiol cypionate (ECP), and estradiol benzoate (EB). The first three studies utilized geldings to compare prolactin and luteinizing hormone (LH) concentrations between sulpiride delivered in VS and SAIB, and ECP or EB delivered in SAIB. Sulpiride stimulated (P < .01) prolactin similarly between vehicles. Geldings pre-treated with EB had higher (P < .05) prolactin responses to sulpiride compared to ECP-treated geldings on days 5, 6 and 9. Both estradiol-sulpiride treatments stimulated LH with no differences between ECP and EB. Experiment 3 compared a simultaneous injection of EB-sulpiride to a non-simultaneous injection (one day apart) of EB-sulpiride. Prolactin was stimulated (P < .05) in both treatment groups, but the response lasted 2 days longer in geldings treated a day apart. Plasma LH increased (P < .01) in both groups equally for 10 days. Experiment 4 applied simultaneous and non-simultaneous EB-sulpiride treatments to seasonally anovulatory mares to induce ovarian activity. Prolactin and LH were stimulated similarly between treatments; however, non-simultaneously treated mares tended (P = .07) to have an ovarian response earlier. In conclusion, SAIB was a suitable vehicle for administration of estradiol and sulpiride and could be an alternative to VS for sustained-release drug delivery.

Effects of Various Methods of Sulpiride Administration on Prolactin Release in Horses

Four experiments assessed factors affecting prolactin responses to sulpiride administration in horses. Experiment 1 compared the efficacy of the (-) enantiomer of sulpiride to that of the commonly used (+/-) racemic mixture. Mares were used in an 8 × 8 Latin square to compare the prolactin responses to four doses of levosulpiride to four corresponding doses of the racemic mixture at twice the dose. Responses at each dose indicated equal and similar (P > .1) responses. Experiment 2 compared the efficacy of 1 gram of orally administered racemic sulpiride to 100 mg of intramuscularly injected sulpiride in oil in mares primed with 50 mg of estradiol cypionate (ECP). Prolactin responses in groups receiving sulpiride were robust but similar in magnitude with minor differences in timing. In experiment 3, ECP-primed geldings received subcutaneous injections of 1.8 grams racemic sulpiride in vegetable shortening in one of three sites: the neck, the back below the withers, or the lower girth region; control geldings received no sulpiride. Prolactin responses to sulpiride lasted a minimum of 96 hours. In experiment 4, prolactin responses to 3 g of racemic sulpiride in vegetable shortening were compared to similar injections (3 g) in 5 mL of sucrose acetate isobutyrate (SAIB; SucroMate) or just SAIB (control) in ECP-primed geldings. Controls had no prolactin response to SucroMate, whereas both treatment groups had extended prolactin responses lasting at least 10 days. It is concluded that prolactin responses to sulpiride in horses can be greatly extended by using hydrophobic vehicles like vegetable shortening or SAIB.

Effects of Combined Estradiol-Sulpiride Treatment and Follicle Ablation on Vernal Transition in Mares: Evaluation of Plasma and Follicular Fluid Hormones and Luteinizing Hormone Receptor Gene Expression

This experiment assessed the hormonal production, secretory aspects, and changes in luteinizing hormone (LH) receptor gene expression of early induced ovulatory-sized follicles relative to the first ovulatory-sized follicles occurring naturally in the spring. Anovulatory mares were treated on January 21 with (1) 50 mg of estradiol cypionate (ECP, n = 8) alone or (2) with ECP followed by two 3-g sulpiride injections (n = 8), 5 and 12 days later. Half of each group also received complete follicle ablation via transvaginal aspiration before ECP treatment. Ovaries were scanned regularly until detection of a 32-35 mm follicle; follicular fluid was recovered via aspiration for analysis of hormonal concentrations. Blood was collected regularly to characterize plasma prolactin, LH, follicle stimulating hormone, progesterone, and estradiol concentrations. Mean date to first 35-mm follicle was earlier (P < .05) in sulpiride-treated mares: five of eight (63%) responded within 28 days of the first sulpiride injection. Ablation did not affect ovarian response. Plasma prolactin was stimulated (P < .0001) in ECP-sulpiride-treated mares for 16 days but did not dictate ovarian response. Estradiol stimulated plasma LH (P < .05), which was higher (P < .05) in treated mares that responded. There was no effect of treatment or ablation on follicular fluid concentrations of estradiol, progesterone, leptin, or insulin-like growth factor 1 or on LH receptor gene expression. These latter similarities indicate that ECP-sulpiride early induced follicles have apparently reached a degree of maturity equivalent to naturally occurring ovulatory-sized follicles later in the spring.