tea and coffee inhibit the secretion of tropic hormones
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Answer:
We studied the effects of acute, intraperitoneal administration of caffeine on serum thyrotropin (TSH), growth hormone, prolactin, thyroxine and 3,3',5-triiodothyronine in rats. Caffeine lowered serum TSH and GH in a dose-dependent manner with ED50 values of 30 and approximately 50 mg/kg, respectively. TSH levels were depressed 1 to 6 hr after injection and correlated with serum caffeine levels greater than 20 micrograms/ml. The decrease in serum TSH was followed by decreases in serum 3,3',5-triiodothyroxine and thyroxine 4 hr after caffeine administration. Theophylline and theobromine had effects similar to those of caffeine on hormone levels. Caffeine did not significantly affect hormone secretion when incubated directly with rat pituitaries in vitro. Administration of antisomatostatin antiserum to rats blocked the inhibitory effects of caffeine on serum GH levels, suggesting that caffeine inhibits GH and TSH secretion by releasing hypothalamic somatostatin.
Answer:
Tropic hormones are hormones that have other endocrine glands as their target. Most tropic hormones are produced and secreted by the anterior pituitary. 719 The hypothalamus secretes tropic hormones that target the anterior pituitary, and the thyroid gland secretes thyroxine, which targets the hypothalamus and therefore can be considered a tropic hormone.
The term tropic is from Ancient Greek in the sense "of or pertaining to a turn or change", meaning "causing a change, affecting"; this is the same origin as tropic and trope. This should not be confused with trophic, as in similar-sounding trophic hormone – the words and concepts are both unrelated. Tropic hormones are contrasted with non-tropic hormones, which directly stimulate target cells.