Differential responses of the somatotropic and thyroid axes to environmental temperature changes in the green iguana

Faecal Triiodothyronine Hormone Levels in Female Iguana during Weekday and Weekend in In Situ Conservation

“…TRH is secreted by the hypothalamus after exposure to stress, illness, cold, metabolic demand, or decreased circulating thyroid hormones, mainly T3. TRH stimulates the pituitary to release TSH, which causes the release of T3 and T4 (6). Other conditions that can affect this axis include drugs, illness, thyroid disease, pituitary disorders, and age.…”

Differential peptide-dependent regulation of growth hormone (GH): A comparative analysis in pituitary cultures of reptiles, birds, and mammals

“…Some of these actions are conserved among vertebrates, although there are also species-specific actions; for example, GH is involved in the acclimatization to saltwater in teleosts ([ [14] , [15] , [16] ]). Furthermore, it has been previously described in fish and in the green iguana (an ectothermic reptilian species belonging to the Squamata order) that circulating levels of GH significantly increased when animals were exposed to changes in environmental temperature, likely as an adaptive mechanism ([ [17] , [18] , [19] ]). This diversity in GH actions could be related to the complex mechanisms involved in the regulation of its synthesis and secretion in the pituitary somatotrophs, which are essentially controlled by several hypothalamic neuropeptides and other factors ([ [20] , [21] , [22] ]).…”

“…On the other hand, a significant increase in the gh mRNA expression and GH release was observed when these reptiles were exposed to low environmental temperatures, an effect where other GH-regulatory peptides (i.e. TRH, PACAP), in addition to GHRH, were apparently involved [ 19 ], showing a contrasting response to what has been reported in mammals [ 55 ]. Thus, we hypothesized that during vertebrate evolution the various GH regulatory peptides may have a distinct participation, and exert differential roles, in controlling the mechanisms implicated in pituitary GH synthesis and secretion.…”