Thyroid Hormone + Growth Hormone – If You Aren’t Using T4 with Your GH, You’re Not Doing It Right
As we learned in high-school Biology class, the body likes to maintain homeostasis, or “normal” operating conditions. This is the body’s version of the status quo, and it fights like hell to maintain the comfort of the status quo (much like moderators on most steroid discussion boards). What we see with thyroid/GH interplay is that physiological levels of circulating thyroid hormones are necessary to maintain normal pituitary GH secretion, due to their directly stimulatory actions. However, when serum concentrations of thyroid hormone increase above the normal range we see an increase in hypothalamic somatostatin action, which suppresses pituitary GH secretion and overrides any stimulatory effects that the thyroid hormone may have had on GH. The suppression of GH secretion by thyroid hormones is probably mediated at the hypothalamic level by a decrease in GHRH release(5).
In addition, as IGF-I production isincreased in the hypothalamus after T3 administration and T3 may participate in IGF-1 mediated negative feedback of GH by triggeringeither increased somatostatin tone and/or decreased GHRH production (6). IGF, interestingly, has the ability to mediate some of T3’s effects independent of GH, but not to the same degree GH can (7.) In fact, IGF-I production isincreased in the hypothalamus after T3, administration it may plausibly participate in negative feedback by triggeringeither increased somatostatin tone and/or decreased GHRH production.So we know that GH lowers T4 (more about this in a sec), but an increase in T3 upregulates GH receptors (8) as well as IGF-1 receptors (9,10).
So what are we doing when we add T3 to GH? We’re effectively shutting down the conversion pathway that is responsible for some of GH’s effects! And what would we be doing if we added in T4 instead of T3? You got it- we’d be enhancing the pathway by allowing the GH we’re using to have more T4 to convert to T3, thus giving us more of an effect from the GH we’re taking. Adding T4 into our GH cycles will actually allow more of the GH to be used effectively!
