Postnatal changes in testicular gonadotropin receptors, serum gonadotropin, and testosterone concentrations and functional development of the testes in bulls

Abstract

The primary objectives of this study were to follow the temporal patterns of testicular LH and FSH receptor (LH-R and FSH-R) concentrations and affinity (K a ) during sexual maturation in bulls and to see if such patterns could help explain the control of rapid testicular growth that occurs after 25 weeks of age, when serum gonadotropin concentrations are low. Separate groups of Hereford!Charolais calves (nZ6) were castrated every 4 weeks from 5 to 33 weeks of age and at 56 weeks of age. A week prior to castrations, from 5 to 33 weeks of age, blood was collected every 15 min for 10 h. The transition from indifferent supporting cells to Sertoli cells in seminiferous tubules was rapid between 13 and 25 weeks and rapid testis growth occurred after 25 weeks of age. Serum LH and FSH concentrations were transiently elevated at 12 weeks of age (P!0.05). LH-R concentrations decreased from 13 to 25 weeks of age and increased to 56 weeks of age (P!0.05). LH-RK a decreased from 9 to 17 weeks of age, increased to 29 weeks of age and declined to 33 weeks of age (P!0.05). FSH-R concentrations declined from 17 to 25 weeks of age then increased to 56 weeks of age (P!0.05). FSH-RK a increased from 17 to 25 weeks of age (P!0.05). High concentrations of gonadotropins and their receptors may be critical to initiate testis growth postnatally and support it after 25 weeks of age in the face of low serum gonadotropin concentrations.

Effect of vaccination against gonadotropin-releasing factor (GnRF) with Bopriva® in the prepubertal bull calf

“…Control animals showed a continuous increase of LH to levels of 0.3 ng/mL serum. These values are much lower than concentrations of about 1.6 ng/mL reported in previous studies (Evans et al, 1993;Bagu et al, 2006), the reason being most likely due the method of LH analysis used, breed differences and most important the frequency of blood sampling. In the experiments mentioned above blood was collected at short intervals of 10-12 min during several hours and the basal, amplitude and mean concentrations of LH determined.…”

“…In the experiments mentioned above blood was collected at short intervals of 10-12 min during several hours and the basal, amplitude and mean concentrations of LH determined. This approach allows detecting increases in LH pulse frequency which is mainly responsible for the prepubertal gonadotropin rise (Evans et al, 1993) reported in previous studies (Aravindakshan et al, 2000;Bagu et al, 2006;Chandolia et al, 1997;Evans et al, 1993). A possible cause for the different findings may be breed influence, as our experiment was performed with Holstein calves whereas Hereford (Chandolia et al, 1997;Evans et al, 1993) or crossbreeds of Hereford and Charolais (Aravindakshan et al, 2000;Bagu et al, 2006) were used in the previous studies.…”

“…This approach allows detecting increases in LH pulse frequency which is mainly responsible for the prepubertal gonadotropin rise (Evans et al, 1993) reported in previous studies (Aravindakshan et al, 2000;Bagu et al, 2006;Chandolia et al, 1997;Evans et al, 1993). A possible cause for the different findings may be breed influence, as our experiment was performed with Holstein calves whereas Hereford (Chandolia et al, 1997;Evans et al, 1993) or crossbreeds of Hereford and Charolais (Aravindakshan et al, 2000;Bagu et al, 2006) were used in the previous studies. Moreover, it has been known that diet and weight gain may also influence LH secretion and the attainment of puberty (Barth et al, 2008;Brito et al, 2007aBrito et al, , 2007b.…”

“…In bull calves, blood concentrations of gonadotropins increase long before the animal reaches puberty. It has been shown that LH starts to rise from 6 weeks of age reaching peak values between 12 to 16 weeks and subsequently drops to basal concentrations at week 25 of life remaining low until attainment of puberty (Amann and Walker, 1983;Aravindakshan et al, 2000;Bagu et al, 2006;Evans et al, 1996;Lacroix and Pelletier, 1979;McCarthy et al, 1979;Rawlings and Evans, 1995;Rawlings et al, 1978Rawlings et al, , 2008Rodriguez and Wise, 1989). The early rise in gonadotropin secretion seems to be essential for normal testicular development and reproductive maturation in bull calves Rawlings et al, 2008).…”

Peri-conception and first trimester diet modifies reproductive development in bulls

“…The relationship between reduced FSH and delayed postnatal activation of the reproductive axis observed in the pubertal and postpubertal LPeri cohort concurs with previous research: FSH levels, along with LH, rise transiently between 1 and 4 months of age in the prepubertal bull (Rawlings et al 1978;Evans et al 1996;Moura and Erickson 1997;Kaneko et al 2001;Bagu et al 2006), a rise reported to be associated with the initiation of rapid testis growth (Moura and Erickson 1997). FSH levels then fall, remaining low during peri-puberty and puberty (Moura and Erickson 1997;Kaneko et al 2001;Brito et al 2007cBrito et al , 2007d.…”