ISSN:
0003-276X
Keywords:
Thyroid follicular cells
;
Ultrastructure
;
Thyroxine
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Medicine
Notes:
Background: The onset of thyriod function occurs at different times with respect to birth in different mammals. In most marsupials studied thus far, thyroid function begins during the latter half of pouch life. However, in marsupials, thyroxine can be transported from the mother to the young via milk. In this study the plasma concentration of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3), in the young was correlated with the ultrastructural appearance of the thyroid of the young.Methods: Thyroid glands at 40, 65, 70, 96, 113, 115, and 129 days postpartum and from an adult were examined with the light and electron microscope. Plasma concentrations of both T4 and T3 in young possums were determined by radioimmunoassay.Results: Plasma concentrations of T4 in the young were less than 10 ng/ml prior to day 60 and 12 ng/ml on day 60; they rose to a peak of 45 ng/ml on day 120 postpartum and then diminished to below 10 ng/ml by day 160 postpartum. Plasma T3 concentrations were similar in profile, the peak concentration being 0.25 ng/ml on day 120 postpartum, and, as with T4, T3 concentrations decreased in the latter part of the lactation period. The morphology of the follicular cells of the thyroid gland would suggest that the developing brushtail possum is capable of producing thyroxine at about day 65 postpartum. Densely staining bodies, presumably lysosomes that are required for the conversion of thyroglobulin to thyroxine, were first seen on day 65, and greater quantities were noted in day 96, 113, 115, and 129 thyroid tissue.Conclusions: The plasma concentrations of T4 and T3 of the young are greater than that of the adult by day 60 postpartum, with peak concentrations of thyroid hormones on day 120 postpartum. Ultrastructural examination would suggest that the possum thyroid gland is capable of producing thyroid hormones at about day 65 postpartum. The activation of the thyroid gland precedes the reported increase in growth rate of the young possum on day 96 (Gemmell and Hendrikz, 1993. Aust. J. Zool., 41:141 - 149 ). © 1995 Wiley-Liss, Inc.
Additional Material:
11 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/ar.1092430212
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