Homeostatic mechanisms controlling growth hormone involve negative feedback by GH and what other hormone?

Growth-hormone-inhibiting hormone or somastostatin.

Explanation:

Basically the GH is secreted by the anterior pituitary glands under the regulations of  certain  secretory nuclei in the  hypothalamus.The cells of these nuclei  secrets  two hormones,

1. growth hormones releasing hormone which stimulate growth hormones releasing-receptors  receptors for the pituitary glands to secrets growth hormones,

and

2. the Growth-hormones-inhibiting hormones. This hormone is   secreted, and carried in the blood stream by hypothalamo-hypophsial-portal circulation in response to elevated levels of GH. They  inhibit the secretion of   Growth hormones  in  the pituitary glands;by inhibiting the activities of growth-hormones -releasing hormone, preventing them from binding with growth-hormone-releasing hormones receptors in the  anterior pituitary gland,therefore inhibiting   GH  secretions .