Decrease of hypothalamic TRH levels but not plasmatic TSH levels after ablation of submandibular salivary glands in the rat.

Abstract

Indirect relationships are thought to exist between submandibular salivary glands (SSG) and the central nervous system (CNS) via superior cervical ganglia (SCG). To study this topic, the concentrations of thyrotropin releasing hormone (THR) and somatostatin (SRIF) were measured in both whole and specific areas of the hypothalamus, as well as plasmatic thyrotropin stimulating hormone (TSH) levels following ablation of SSG. Twenty, forty and fifty days after ablation of SSG, groups of operated and sham-operated animals weighing 230-260 g at the beginning of experimentation, were killed by cervical dislocation. Plasma was taken, frozen and stored for TSH-radioimmunoassay (RIA) and the hypothalami were removed and homogenized in either 0.1 N HCl (for TRH-RIA) or 0.2 N acetic acid (for SRIF-RIA). Twenty days after ablation of SSG in another group, TRH concentrations were measured in both the median eminence (ME) and the paraventricular nucleus (PVN), dissected by the micropunch technique. The results show that twenty days after SSG ablation, the hypothalamic TRH concentrations was significantly lower in operated than in sham-operated animals (295.2 +/- 24.8 vs 226 +/- 11.15 pg/mg hypothalamus respectively p less than 0.01, n = 9). No differences were observed at later intervals. This finding seems to be specific for this peptide since the SRIF level was not modified twenty days after SSG removal. Among the discrete hypothalamic areas examined, only the ME exhibited a significant decrease in TRH content (25.43 +/- 3.02 ng/mg prot. VS. 41.24 +/- 1.33 ng/mg prot., respectively). Despite these results on TRH levels, no modifications in plasmatic TSH levels were observed.(ABSTRACT TRUNCATED AT 250 WORDS)