Long-term growth after hypophyseal stalk transection and hypophysectomy ofbeef calves

Hypothalamic hormones regulate episodic and basal secretion of hormones fro m the anterior pituitary gland that affect metabolism and growth in cattle. This study focused on long-term growth in young calves subjected to hypoph ysectomy (HYPOX), hypophyseal stalk transection (HST), and sham operation c ontrol (SOC). Cross-bred (Hereford x Aberdeen Angus) and Hereford, and Aber deen Angus calves were HYPOX (n = 5), HST (n = 5), or SOC (n = 8) at 146 +/ - 2 days of age, whereas another group was HST (n = 5) or SOC (n = 7) at 27 3 +/- 5 days of age. Body weight was determined every 21 days from birth to 1008 days of age. Anterior vena cava blood was withdrawn at 4-day interval s from day 64-360 for RIA of GH, TSH, T-4,, T-3,, and LH, and at 20-min int ervals for 480 min to determine episodic hormone secretion. Daily feed inta ke was determined in HST and SOC calves during an 80-day period. Birth weig ht averaged 35 +/- 1 kg (+/- SE and was 142 +/- 4 kg at 126 days and 208 +/ - 8 kg at 252 days before surgery. From day 146-1008, growth was arrested ( P < 0.001) in HYPOX (0.06 +/- 0.01 kg/day) compared with SOC (0.50 +/- 0.04 kg/day) calves. Growth continued but at a significantly lower rate (P < 0. 05) in calves HST at 146 days (0.32 +/- 0.07 kg/day) and 273 days (0.32 +/- : 0.06 kg/day) compared with SOC (0.50 +/- 0.09 kg/day). Growth continued t o be impaired to 1008 days, but more so in those HST at 146 days (432 +/- 4 3 kg BW) than 273 days (472 +/- 5 kg BW)? and less (P < 0.05) than SOC (586 +/- 37 kg BW). Daily feed intake was consistently less (P < 0.05) in HST c ompared with SOC calves. Although episodic GH secretion was abolished and p eripheral serum GH concentration remained consistently lower in HST (2.4 ng /ml) than SOC (5.5 ng/ml; P < 0.01), the calves continued to grow throughou t 1008 days. Peripheral serum TSH concentration was less (P < 0.05) HST com pared with SOC calves. There was an abrupt decrease (P < 0.001) in serum T- 4, (4-fold) and T-3, (3-fold) concentration after surgery that remained to 360 days in HST compared with SOC calves. At the time calves were killed, p ituitary gland weight was markedly reduced (P < 0.001) in HST(0.18 +/- 0.01 g/100 kg BW) compared with SOC (0.54 +/- 0.03 g/100 kg BW). Histological e xamination of pituitary glands from HST calves indicated the persistence of secretory GH and TSH cells in the same areas of the adenohypophysis as SOC calves. Coronal sections of the gland stained with performic acid-Alcian b lue-periodic acid-Schiff-orange G, revealed GH and TSH secreting cells in H ST calves similar to controls. These results indicate that long-term growth continues, but at a slower rate, after hypophyseal stalk transection of im mature calves in spite of complete abolition of episodic GH secretion and c onsistently decreased basal secretion of GH, TSH, T-4, and T-3 compared wit h sham-operated animals. Growth was abolished after hypophysectomy of immat ure calves in which circulating GH and TSH was undetectable.