SRIF-sensitive compartmentalization of stored rGH is abolished by hypothyroidism.
Rat adenohypophyses lose immuno- and bioassayable growth hormone in hypothyroidism. We examined whether the somatotroph also loses mechanisms for intracellular hormone compartmentalization during hypothyroidism. A series of identical perifusions was performed using pituitary tissue from thyroidectomized rats before and after thyroxine replacement. Somatostatin (SRIF), (Bu)2cAMP and potassium ion were employed to produce a wide range of hormone release responses. Growth hormone synthesis diminished with hypothyroidism and increased with thyroid hormone replacement. Growth hormone release was therefore expressed as a percent of pituitary content to circumvent effects of variable content. Post-somatostatin rebound release was lost in hypothyroidism: it fell progressively after thyroidectomy (day 7 = 45% of control; day 14 = 11%; day 71 = 3%) and was restored by thyroxine replacement (day 2 = 24%; day 5 = 50%; day 9 = 102%). In conclusion, hypothyroid somatotrophs lose the ability to sequester stored hormone in a SRIF-sensitive compartment. Thyroxine replacement restores that capability. Thus, SRIF-sensitive rGH compartmentalization is thyroid hormone dependent.
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D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002451:Cell Compartmentation; D013006:Growth Hormone / Q000096:biosynthesis / Q000378:metabolism*; D007037:Hypothyroidism / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013004:Somatostatin / Q000494:pharmacology*; D013965:Thyroidectomy; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000494:pharmacology / Q000502:physiology*; D013997:Time Factors
D013004:Somatostatin; D003994:Bucladesine; D013972:Thyrotropin; D013006:Growth Hormone; D013974:Thyroxine; D011188:Potassium