368 CELLS, TISSUES, AND ORGANISMS 



by peripheral tissues. To this end, the epididymal adipose tissues of 

 normal, hypophysectomized, and hypophysectomized growth-hormone- 

 treated rats were excised, incubated in a suitable medium, and the 

 release of FFA by the tissues into the medium was measured. It was 

 found that hypophysectomy greatly reduced the release of fatty 

 acids from adipose tissue, and that the administration of growth 

 hormone, chronically or acutely, to hypophysectomized animals re- 

 turned the FFA release toward normal (Table II). These experiments 

 strongly suggest that growth hormone increases the mobilization of 

 fatty acids from adipose tissue and that this increased mobilization in 

 turn leads, at least temporarily, to a rise in circulating FFA (Knobil, 

 1959), thus confirming the conclusions based on earlier studies employ- 

 ing less direct evidence ( see de Bodo and Altzuler, 1957 ) . Whether this 

 eflFect of growth hormone represents a direct or primary action of the 

 hormone on adipose tissue or whether fatty-acid mobilization from 

 adipose tissue is secondary to its protein anabolic or other metabolic 

 action is still open to question. 



When growth hormone is added directly to one of a pair of 

 epididymal adipose tissues exercised from the same animal, an increase 

 in FFA release into the medium is clearly demonstrable (Table III). 

 The minimal efiFective concentration varies with the growth-hormone 

 preparation used. In the case of bovine growth hormone, a concentra- 

 tion of 50 micrograms per ml. is required for a unequivocal lipolytic 

 effect, whereas one microgram per ml. of a simian growth-hormone 

 preparation is invariably efiFective. While such low concentrations may 

 at first glance meet the requirements for what is generally acceptable 

 as "physiological," they by no means prove the in vitro lipolytic eflFect 



TABLE II 



Effect of Hypophysectomy and Growth-Hormone Treatment on 

 FFA Release by Adipose Tissue 

 (From Knobil, 1959) 



FFA Release 

 Rats jLteq/gm/hour 



Normal controls 5.79 ±: .44* 



Hypox + saline 0.90 ± 16 



Hypox + G.H. 2.30 ± .37 



(3 mg./rat 3 hr. before 



sacrifice) 

 Hypox + G.H. 3.40 ± .66 



(3 mg. /rat/day for 3 days) 



" Mean ± S.E. 



