Iron Content of Rat Serum Ferritin.

Abstract

ABSTRACT. The serum ferritin concentration was significantly higher in female than in male rats, reflecting higher iron stores in females than in males. The mean iron/protein ratio of serum ferritin was 0.018 ± 0.008 (SD) (µg of Fe/µg of protein) in female rats and 0.011 ± 0.011 in male rats, being much lower than that of liver ferritin (0.233 ± 0.014 in females and 0.227 ± 0.020 in males). Iron loading of rats significantly increased serum ferritin concentration, but did not influence the iron content of serum ferritin. These results indicate that rat serum ferritin contains only a small amount of iron independent of body iron stores. KEY WORDS: ferritin iron, rat, serum ferritin.J. Vet. Med. Sci. 63(5): 587-589, 2001 Ferritin is a major iron-storage protein that is composed of 24 subunits of two types, termed H and L, the molecular masses of which are 21 kDa and 20 kDa, respectively [4,8,16]. Ferritin is present not only in cells but also in sera, and the serum ferritin level is positively correlated with body iron stores [1-3, 12, 15, 18]. The major function of tissue ferritin is to detoxify and store intracellular iron [8], and it contains a large amount of iron [5,14,17]. Serum ferritin has been found to have different amounts of iron in some mammals [6,9,13,20,22]. The physiological significance of serum ferritin and its iron remains unclear. Although rat serum ferritin was purified by Halliday et al. [7], its iron has yet to be determined. In the present study, the iron content of rat serum ferritin was measured, and compared with that of serum ferritin from other mammals.Female and male Wistar rats aged 9-12 weeks (Clea Japan, Tokyo, Japan) were used. Male rats were iron-loaded by intraperitoneal injection of iron dextran (100 mg iron/ml; Sigma, St. Louis, MO, U.S.A.) to increase body iron stores. Rats received single doses of 7 mg of iron three times on alternate days. Control rats were injected with an equivalent volume of 0.9% NaCl. Blood samples and livers were collected 2 days after the final administration from the untreated and iron-loaded rats under pentobarbital-induced anesthesia prior to sacrifice. The serum samples and tissues were stored at -25°C until use.Ferritin was purified from rat livers as previously described [19]. Protein was determined according to the method of Lowry et al.[11] using bovine serum albumin as a protein standard. Rabbit antisera to rat liver ferritin were prepared, and antibodies to the ferritin were purified from the antisera by affinity chromatography as described previously [19].Each rat liver was homogenized in a Waring blender for 3 min with 10 volumes of 10 mM Tris containing 0.2 mM Pefabloc SC (Merck, Darmstadt, Germany) as a serine proteinase inhibitor. Each homogenate was divided into two parts; one was used for measuring non-heme iron; and the other was centrifuged at 24,000 × g for 20 min at 4°C, then the supernatant (liver extract) was used for measuring ferritin protein and ferritin iron. Total non-heme iron in liver homogenates was measured as previo...

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