Neuropeptide stimulation of thyrotropin secretion in the larval bullfrog: Evidence for a common neuroregulator of thyroid and interrenal activity in metamorphosis
✍ Scribed by Denver, Robert J. ;Licht, Paul
- Publisher
- John Wiley and Sons
- Year
- 1989
- Tongue
- English
- Weight
- 420 KB
- Volume
- 252
- Category
- Article
- ISSN
- 0022-104X
No coin nor oath required. For personal study only.
✦ Synopsis
The effects of several neuropeptides on in vitro thyrotropin (TSH) secretion by pituitaries of the frog Rana catesbeiana were studied at two stages of development. The relative concentration of TSH secreted into the medium was determined by bioassay using in vitro thyroxine (T4) production by thyroids from adult grass frogs, Rana pipiens. Pituitaries from tadpoles in Taylor-Kollros stages 17-19 responded to doses of ovine corticotropin-releasing hormone (CRH) ranging from 10 t o 1,000 ngiml; the same glands did not respond t o doses of thyrotropin-releasing hormone (TRH) between 10 and 1,000 ngiml. A single dose of 1,000 ngiml rat growth hormonereleasing hormone (GHRH) had no effect on TSH release. Pituitaries from postmetamorphic frogs (stage 25) exposed to 1,000 ng/ml ovine CRH secreted concentrations of TSH that were higher on average than controls (four of seven responded), and two of seven responded to 100 ng/ml TRH. These observations raise the possibility for a common central regulator of the thyroid and interrenal axes in metamorphosis in which a CRH-like molecule might act as an important neuroendocrine stimulus for both corticotropin and thyrotropin secretion. Furthermore, these and previous results with several species of adult anurans (R.J. Denver: Gen. Comp. Endocrinol., suggest that pituitary TSH responsiveness t o TRH develops in frogs after metamorphic climax.