Bovine serum hormone concentrations after thyroprotein and thyrotropin releasing hormone

Serum hormones during the estrous cycle and estrous behavior in heifers after administration of propylthiouracil and thyroxine

Two experiments were conducted to assess the characteristics of thyroid-stimulating hormone (TSH) during the estrous cycle and to examine the effects of experimentally altered thyroid status on estrous behavior and hormonal concentrations in heifers. In Exp. 1, normal profiles of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and TSH were examined on days 2, 12, and 19 of the estrous cycle (day 0 = estrus) in six Holstein heifers. Baseline concentrations of LH were 1.5- to 2.1-fold higher on day 2 (P = .07) and day 19 (P < .01) than on day 12. Pulse frequency of LH was higher (P < .05) on days 12 and 19 than on day 2. For FSH, baseline concentrations were similar on all 3 d, but pulse frequency was higher (P < .05) on day 19 than on day 2 or day 12. Overall and baseline concentrations of TSH were similar on all 3 d. Pulse frequency of TSH was higher (P < .05) on day 12 than on day 19, but both were similar to that on day 2. In Exp. 2, secretion of TSH in Holstein heifers was altered by administering (i.v.; one-half of the daily dose given twice daily) either phosphate-buffered saline (SAL; n = 6), propylthiouracil (PTU; 20 mg/100 kg body weight [BW]; n = 6), or T4 (1 mg/100 kg BW; n = 5) from day 4 until the next estrus. Duration of estrous cycles during and after treatments, percentages of heifers exhibiting estrus, BW, and average daily gain were unaffected by treatment. Concentrations of TSH were higher (P < .05) in the afternoon than in the morning and higher (P = .06) in PTU heifers than in T4 heifers. Treatment with T4 during the treatment estrous cycle and for up to 6 d into the next estrous cycle increased (P < .01) concentrations of T4 and T3 compared to SAL and PTU. Treatment with PTU during the treatment cycle increased concentrations of T4 (P < .05) and TSH (P = .06) compared to SAL. We conclude that TSH secretion was pulsatile, demonstrated a diurnal change, and varied inconsistently during the estrous cycle. Altering thyroid hormones and TSH secretion in heifers seemed to have no effect on estrous behavior or estrous cycles.

Effect of long-term administration of human growth hormone-releasing factor and (or) thyrotropin-releasing factor on hormone concentrations in lactating dairy cows

Fifteen cows (87 +/- 8 d in lactation; 641 +/- 33 kg BW) were randomly assigned to treatment and then subjected for 182 d to daily sc injection (1000 hr), in the cervical area, of saline (control), thyrotropin-releasing factor (TRF: 1 micrograms/kg BW), growth hormone-releasing factor (1-29)NH2 (GRF; 10 micrograms/kg BW) or GRF plus TRF (10 and 1 micrograms/kg BW, respectively) according to a 2 x 2 factorial design. On days 1, 31, 88 and 179, jugular blood samples were collected from 2 hr before to 6 hr after injection. Samples were also collected for 5 consecutive days after cessation of treatment. GRF always induced growth hormone (GH) release (600 vs 7925 ng.min/ml) with augmentation of response with time (interaction GRF * day; P less than .001). TRF did not affect (P greater than .25) GH release; there was no interaction (P greater than .25) with time. There was no significant interaction (P greater than .25) between GRF and TRF on GH release. However, the amount of GH release with GRF plus TRF was always greater than with GRF alone (9419 vs 6431 ng.min/ml). TRF induced a significant release of prolactin (23769 vs 42175 ng.min/ml) but GRF reduced the amount of prolactin release on the last day of sampling. TRF induced thyroid stimulating hormone (TSH) release only on the first day of injection while triiodothyronine (T3) and thyroxine (T4) continued to respond to TRF throughout the treatment period. Concentrations of T3 and T4 fell below control levels after cessation of TRF injection. In conclusion, GRF-induced GH release and TRF-induced Prl and thyroid hormone release were maintained over a 6-mo treatment period. TRF induced TSH release only on the first day of injection. Overall, these results raised the possibility of a direct effect of TRF on the thyroid gland.

Synergism and diurnal variations of human growth hormone-releasing factor (1-29)NH2 and thyrotropin-releasing factor on growth hormone release in dairy calves

Sixteen male Holstein calves averaging 168 kg body weight (BW) were used to determine the effects of human growth hormone-releasing factor (1-29)NH2 (hGRF (1-29)NH2; .22 micrograms/kg BW), thyrotropin-releasing factor (TRF; .165 micrograms/kg BW) or hGRF (1-29)NH2 plus TRF (.22 and .165 micrograms/kg BW, respectively) on growth hormone (GH) release in animals exposed to 16 hr of light (L): 8 hr of dark (D) (lights on at 0100 hr) and hGRF plus TRF (.22 and .165 micrograms/kg BW, respectively) in animals exposed to 8L:16D (lights on at 0900 hr). For each treatment, times of iv injection were 0400, 1000, 1600 and 2200 hr. In animals exposed to 16L:8D, average GH peaks reached after hGRF (1-29)NH2 or TRF injections were 49.7 and 32.0 ng/ml while the area under the GH response curve (AUC) were 1247 and 1019 ng/ml.min, respectively. There was no significant effect of times of injection on GH release following the separate injection of hGRF(1-29)NH2 or TRF. In animals exposed to 16L:8D, GH peaks and AUC after hGRF plus TRF injections were 226.4, 189.2 and 116.8 ng/ml, and 4340, 3660 and 2415 ng/ml.min at 0400, 1000 and 1600 hr (lights on), respectively but only 42.3 ng/ml and 1692 ng/ml.min at 2200 hr (lights off). In animals exposed to 8L:16D, GH levels and AUC after hGRF plus TRF injections reached 177.5 and 180.5 ng/ml, and 2759 and 3704 ng/ml.min at 1000 and 1600 hr (lights on) but only 84.0 and 72.7 ng/ml, and 1544 and 1501 ng/ml.min at 0400 and 2200 hr (lights off), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone secretion in anaesthetized fowl. 1. Refractoriness to repeated stimulation by human pancreatic growth hormone-releasing factor (hpGRF) or thyrotrophin releasing hormone (TRH)

The intravenous (iv) administration of thyrotrophin releasing hormone (TRH, at 1.0 or 10.0 micrograms/kg) or human pancreatic growth hormone-releasing factor (hpGRF(1-44)NH2, at 10 micrograms/kg) markedly increased the growth hormone (GH) concentration in the plasma of immature or adult cockerels anaesthetized by sodium pentabarbitone (30 mg/kg, iv). A second injection of either TRH or hpGRF failed to increase the GH concentration in immature chicks when administered 15, 30, or 60 min after the first injection. However, significant GH responses to TRH or hpGRF were observed when the interval between injections was either 120 or 240 min. The magnitude of the GH responses to TRH were, however, diminished by 83.3 and 26.7% when given 120 or 240 min after the initial TRH injection, and the responses to hpGRF were similarly reduced by 68.3 and 33.6%. A similar period of GH refractoriness to TRH or hpGRF stimulation was also observed in adult birds, although the recovery of GH responsiveness occurred earlier. While a second injection of hpGRF was ineffective in increasing the plasma GH concentration if given within 30 min of the first, it was fully effective when the interval between injections was greater than 60 min. In response to a second injection of TRH, the GH concentration was elevated when the interval between injections was greater than 120 min, after which the magnitude of the response evoked was greater than that induced by the initial injection. Growth hormone secretion secretion in immature and adult fowl is therefore refractory to repeated provocative stimuli, although the mechanism involved is unknown.

Serum thyrotropin, thyroxine, and tri-iodothyronine in dairy cows fed varying amounts of iodine

The objective was to determine whether dairy cows fed supplemental iodine daily at 2.5 or 5.0 mg per kg body weight for 49 wk had altered thyroid status relative to controls fed no supplemental iodine. Average daily dose of iodine was 1.6 and 3.3 g. Iodine as ethylene diamine dihydriodide was fed to Holstein cows beginning at 8 to 10 wk of lactation, for the remainder of that lactation, through the dry period, and into the next lactation. On day 341 after onset of iodine feeding, each cow was injected intravenously with 15 microgram thyrotropin releasing hormone per 100 kg body weight. Thyrotropin in jugular blood collected before injection of releasing hormone averaged 7.6, 6.1, and 8.2 ng/ml for cows given 0, 2.5, and 5.0 mg iodine/kg body weight; there were no differences between means. Releasing hormone increased thyrotropin, thyroxine, and tri-iodothyronine in serum of all cows, but increases were not affected by quantity of dietary iodine.