Concentrations of Prolactin, Luteinizing Hormone and Follicle Stimulating Hormone in Pituitary and Serum of Horses: Effect of Sex, Season and Reproductive State

Abstract

Pituitary and serum from 86 male or female horses of various reproductive states were collected in the normal breeding season (summer) and in the nonbreeding season (winter) at a commercial slaughterhouse. Concentrations of prolactin (PRL), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured by radioimmunoassay. Concentrations of pregnant mare serum gonadotropin and reproductive steroids in serum and gross appearance of the reproductive tract and gonads were used to catagorize reproductive state. Concentrations of PRL were higher (P less than .01) in summer than in winter in pituitary and serum of mares, stallions and geldings. In summer, mares had higher (P less than .01) concentrations of PRL in serum than stallions. In mares, concentrations of LH in pituitary were higher (P less than .05) in summer than in winter. Concentrations of LH in serum were higher (P less than .01) in summer than in winter in mares and geldings, higher (P less than .01) in mares than in stallions in summer, higher (P less than .01) in geldings than in stallions in summer and higher (P less than .01) in mares with low serum progesterone (P) concentrations than in mares with high P concentrations in summer. Concentrations of FSH in pituitary and serum did not differ between summer and winter for any type of horse.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphological Studies on Testicular Development in the Horse.

“…Spermatozoa in testes were seen one year after birth. It takes approximately two years to attain sexual maturation [1], and thereafter the serum concentrations of testosterone, luteinizing hormone, and prolactin are higher in breeding season than in non-breeding season [2][3][4][5][6][7]. Morphometric analysis on some parameters, such as the number of Leydig and Sertoli cells,…”

Dinâmica hormonal durante o processo luteolítico nas espécies equina e bovina; com ênfase sobre o papel da prolactina

“…Os níveis da concentração de PRL são elevados no verão e baixos no inverno (THOMPSON et al, 1986). Durante o período transicional entre a estação anovulatória para a ovulatória, a estimulação da secreção de PRL acelera o crescimento folicular e antecipa a primeira ovulação da estação ovulatória (BESOGNET;HANSEN; NEQUIN et al, 1993;THOMPSON et al, 1986), agindo como um potencial regulador da secreção de gonadotrofinas (GREGORY et al, 2000). Na estação ovulatória, os níveis de PRL são mais elevados no estro do que no diestro (WORTHY et al, 1987;SHAND et al, 2000), sendo observado um efeito positivo da concentração de estradiol sobre a PRL no início da fase luteal (ROSER et al, 1987).…”

“…In horses, the majority of the published studies on PRL are related to pregnancy (AURICH et al, 1995;IRELAND et al, 1991) parturition (WORTHY et al, 1986), and seasonality of reproduction (KING et al, 2010b;JOHNSON, 1986;GREGORY et al, 2000;EVANS et al, 1991;THOMPSON et al, 1986;HOFFMAN Jr;DEPEW, 1997). There is a rise in serum and pituitary PRL concentration in the summer, whereas concentrations are low in winter (THOMPSON et al, 1986).…”

“…There is a rise in serum and pituitary PRL concentration in the summer, whereas concentrations are low in winter (THOMPSON et al, 1986). During the transitional period between the anovulatory and ovulatory seasons, increasing concentration of PRL accelerates follicular growth (BESOGNET; HANSEN; NEQUIN et al, 1993), hastens the ovulatory season (THOMPSON et al, 1986), and plays a potential role in regulation of gonadotropin concentrations (GREGORY et al, 2000). During the early luteal phase, estradiol has a positive effect in regulating PRL release, based on a correlation between estradiol and PRL concentrations in mares (ROSER et al, 1987) and greater PRL concentration during estrus than during diestrus in several species as cattle , sheep (MCNEILLY , 1987;, and horses (WORTHY et al, 1987;SHAND et al, 2000).…”

“…There is a rise in serum and pituitary PRL concentration in the summer, whereas concentrations are low in winter (THOMPSON et al, 1986). During the transitional period between the anovulatory and ovulatory seasons, increasing concentration of PRL accelerates follicular growth (BESOGNET; HANSEN; NEQUIN et al, 1993), hastens the ovulatory season (THOMPSON et al, 1986), and plays a potential role in regulation of gonadotropin concentrations (GREGORY et al, 2000).…”