Pituitary mRNA expression of the growth hormone axis in the 1-year-old intrauterine growth restricted rat

The effect of selective oestrogen receptor antagonists in an in vitro model of growth plate chondrogenesis

While oestrogen is recognized to play a key role in regulating growth, particularly in relation to epiphyseal fusion, the mechanisms that mediate its effects are still unclear. We utilized an in vitro model of chondrogenesis, the RCJ3.1C5.18 cell line, to explore the effect of oestrogen on this process. We demonstrated the presence of oestrogen receptors (ER) α and β in these cells, with increased abundance of both receptor sub-types evident as the cells differentiated. ERα localized to the nucleus, suggesting it was signalling by genomic pathways, while ERβ was seen predominantly in the cytoplasm, suggesting it may be utilizing non-genomic signalling. While exogenous oestrogen had no effect on proliferation or differentiation, we found some evidence for the endogenous production of oestrogen (intracrinology), as suggested by the expression of aromatase in these cells. Selective ERα blockade with methyl piperidinopyrazole (MPP) led to a significant reduction in both proliferation and differentiation, while ERβ blockade with R,R tetrahydrochrysene (THC) led to an increase in these parameters. This is in keeping with results from mouse knockout models suggesting that unopposed ERβ signalling leads to an inhibition of skeletal growth. Our results are further evidence for the importance of differential ER signalling in regulating chondrogenesis. Future studies examining in vivo effects of these agents are required to extrapolate these findings to a mammalian model.

Opposite effects of glucagon and insulin on compensation for spectacle lenses in chicks

PURPOSE

Chick eyes compensate for the defocus imposed by positive or negative spectacle lenses. Glucagon may signal the sign of defocus. Do insulin (or IGF-1) and glucagon act oppositely in controlling eye growth, as they do in metabolic pathways and in control of retinal neurogenesis?

METHODS

Chicks, wearing lenses or diffusers or neither over both eyes, were injected with glucagon, a glucagon antagonist, insulin, or IGF-1 in one eye (saline in the other eye). Alternatively, chicks without lenses received insulin plus glucagon in one eye, and either glucagon or insulin in the fellow eye. Ocular dimensions, refractive errors, and glycosaminoglycan synthesis were measured over 2 to 4 days.

RESULTS

Glucagon attenuated the myopic response to negative lenses or diffusers by slowing ocular elongation and thickening the choroid; in contrast, with positive lenses, it increased ocular elongation to normal levels and reduced choroidal thickening, as did a glucagon antagonist. Insulin prevented the hyperopic response to positive lenses by speeding ocular elongation and thinning the choroid. In eyes without lenses, both insulin and IGF-1 speeded, and glucagon slowed, ocular elongation, but glucagon and insulin each increased the rate of thickening of the crystalline lens. When injected together, insulin blocked choroidal thickening by glucagon, at a dose that did not, by itself, thin the choroid.

CONCLUSIONS

Glucagon and insulin (or IGF-1) cause generally opposite modulations of eye growth, with glucagon mostly increasing choroidal thickness and insulin mostly increasing ocular elongation. These effects are mutually inhibitory and depend on the visual input.