Hypothyroidism increases serotonin turnover and sympathetic activity in the adult rat.
Adult, male Sprague-Dawley rats underwent surgical thyroidectomy (Tx) or sham surgery. In all three experiments from which data are reported, a 3-week recovery period was allowed. In experiments I and II, baseline measurements of colonic temperature (Tc) and urinary norepinephrine excretion (NE) were obtained, and both variables were monitored daily for the duration of the studies. After baseline measurements, half of each surgical group was given either triiodothyronine (T3) or vehicle injections subcutaneously; in experiment I replacements continued for 1.5 days, while in experiment II T3 replacement continued for 3.5 days. Rats were decapitated at the end of each experiment and serotonin (5-HT) turnover was measured in brainstem. Serotonin turnover in rostral and caudal brainstem was increased with Tx (p less than 0.05). Increased turnover in caudal brainstem was normalized by T3 only in experiment II. Similarly, decreased Tc and elevated NE with Tx were normalized in experiment II but not in experiment I. In experiment III, NE measurements normalized on a creatinine excretion basis indicated that increased NE is evident with Tx, irrespective of normalization procedure. Significant correlations between 5-HT in caudal brainstem and metabolic correlates of sympathetic function, concurrent normalization of NE and 5-HT in caudal brainstem, plus work from other laboratories describing sympathoexcitatory serotonergic neurons located in the caudal brainstem suggest that the central and peripheral changes in the hypothyroid rat are causally related.
Henley
W N
WN
Department of Zoology, Ohio University, Athens 45701.
Chen
X
X
Klettner
C
C
Bellush
L L
LL
Notestine
M A
MA
D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D001933:Brain Stem / Q000187:drug effects / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003106:Colon / Q000187:drug effects / Q000502:physiology; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D007037:Hypothyroidism / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D009638:Norepinephrine / Q000652:urine; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism*; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D013974:Thyroxine / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology
D014284:Triiodothyronine; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D013974:Thyroxine; D009638:Norepinephrine