Young female rats of 160-180 g were implanted with osmotic minipumps releasing 3.0 micromol/day per kg of oleoyl-oestrone in liposomes (Merlin-2) into the bloodstream for up to 14 days. Merlin-2 induced a loss of appetite in the first days, later recovered, and a decrease in body weight of 7%, which contrasts with the 15% increase in controls during the 2-week period. Neither plasma glucose nor urea was affected by treatment, but liver glycogen increased by 50% in 14 days. Insulin decreased slightly with Merlin-2 treatment. Plasma corticotropin (ACTH) and corticosterone showed a transient increase by day 6 of treatment. The expression of the ob gene in adipose tissue fell during the period studied to practically nil on day 14; circulating leptin levels decreased more than 70% from day 1 to day 14. Oestrone levels increased from 0.3 nM (controls) to a maintained 40-60 nM level for the rest of the experiment. Oleoyl-oestrone levels first increased 4-fold, to decrease again to the initial levels on day 10, increasing later to 100-fold on day 14. The three phases observed in food intake, weight loss and oleoyl-oestrone levels match fairly well, which supports the direct involvement of oleoyl-oestrone in body-weight control. However, the control of oleoyl-oestrone levels seems to be mediated in part by corticosterone. The practical disappearance of leptin synthesis coincides with the massive accumulation of oleoyl-oestrone in plasma. The results presented suggest the involvement of oleoyl-oestrone in the main mechanisms of control of body weight and its regulation by glucocorticoids and leptin.

Adipose tissue (AT) is distributed as large differentiated masses, and smaller depots covering vessels, and organs, as well as interspersed within them. The differences between types and size of cells makes AT one of the most disperse and complex organs. Lipid storage is partly shared by other tissues such as muscle and liver. We intended to obtain an approximate estimation of the size of lipid reserves stored outside the main fat depots. Both male and female rats were made overweight by 4-weeks feeding of a cafeteria diet. Total lipid content was analyzed in brain, liver, gastrocnemius muscle, four white AT sites: subcutaneous, perigonadal, retroperitoneal and mesenteric, two brown AT sites (interscapular and perirenal) and in a pool of the rest of organs and tissues (after discarding gut contents). Organ lipid content was estimated and tabulated for each individual rat. Food intake was measured daily. There was a surprisingly high proportion of lipid not accounted for by the main macroscopic AT sites, even when brain, liver and BAT main sites were discounted. Muscle contained about 8% of body lipids, liver 1–1.4%, four white AT sites lipid 28–63% of body lipid, and the rest of the body (including muscle) 38–44%. There was a good correlation between AT lipid and body lipid, but lipid in “other organs” was highly correlated too with body lipid. Brain lipid was not. Irrespective of dietary intake, accumulation of body fat was uniform both for the main lipid storage and handling organs: large masses of AT (but also liver, muscle), as well as in the ”rest” of tissues. These storage sites, in specialized (adipose) or not-specialized (liver, muscle) tissues reacted in parallel against a hyperlipidic diet challenge. We postulate that body lipid stores are handled and regulated coordinately, with a more centralized and overall mechanisms than usually assumed.