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The properties of slightly soluble Zn(II)-protein complexes in the form of a suspension. Slightly soluble Zn(II) complexes with selected hormones were obtained in the form of a suspension. Zn(II)-protein complexes were obtained at different ligand concentrations. The amount of Zn(II) in microM bound to a protein increases along with an increase in the added ligand concentration. This amount is statistically significant as far as its binding to INS is concerned. Proteins bind to Zn(II) through two classes of binding sites (n). Most Zn(II) binds to albumin and least to LH and FSH. The protein molecular weight and number of its amino acid residues have an influence on binding Zn(II) to a selected protein. Zn(II) has the highest affinity for PRL and INS, and the lowest for albumin and FSH. The kinetics analysis of Zn(II) binding to proteins has shown that Zn(II) creates the most stable complexes with PRL, INS, and LH. Relatively, weak complexes were obtained with albumin and FSH. The protein molecular weight and the number of its amino acid residues have a significant influence on the stability of Zn(II)-protein complex. The lower protein molecular weight and number of its amino acid residues, the more stable Zn(II)-protein complex is. The stability of complexes is also associated with the amount of Zn(II) bound to a protein and its affinity for a protein.

The preparation and properties of low soluble, suspended Zn(II) complexes containing the selected peptides: tyroliberin (TRH), gonadorelin (GnRH), dalarelin and corticothropin (ACTH) were studied. The amount of Zn(II) bound by 1 muM of the selected peptide (n) was defined, as well as affinity of Zn(II) to the peptide (Ka) and the durability of the created complex Zn(II)-peptide (Kd). ACTH associated the highest amount of Zn(II), and GnRH the lowest one: 1 microM of ACTH complexed 0.81 microM +/- 0.03 Zn(II), the same quantity of GnRH-0.52 microM +/- 0.07 and TRH and dalarelin associated 0.75+/-0.03 and 0.79+/-0.02 microM of Zn(II), respectively. The closest affinity was stated between Zn(II) and GnRH (Ka=157.692+/-21.300 microM(-1)), the smallest-towards ACTH (Ka=1.136+/-0.042 microM(-1)). The lower amount of Zn(II) associated by the studied peptide, the higher was its affinity versus this metal (r=-0.942). The analysis of the kinetics of the Zn(II)-peptide linkage revealed that the most stable complexes with this metal were formed by GnRH (Kd=0.006+/-0.001 microM(-1)) and by dalarelin (Kd=0.020+/-0.001 microM(-1)). Zn(II) with GnRH complexes are about 147 times more durable than ACTH (Kd=0.880+/-0.033 microM(-1)) ones. It was established that the Zn(II)-peptide complexes were more stable in the case of lower molecular weight of the peptide (r=0.963), and the inferior number of the amino acid residues accessible in the peptide (r=0.967).

A complex coacervation method was used to prepare microcapsules containing 74.8 +/- 1.5% of the 125I labelled dalarelin incorporated in the gelatine-algin coating. Microcapsules (62 +/- 1.7%) formed, did not exceed a size of 108 microm. The high content of the small size allowed this formulation to be administered by intramuscular injection to rats. It was found that the 125I labelled dalarelin in the form of microcapsules had better bioavailability and was active longer in the rat when compared with the 125I labelled dalarelin solution injections. Dalarelin administered in the microcapsular form was characterised by a higher biological availability. The degree of relative biological availability was calculated as 123% for the dalarelin in the microcapsular form.

An investigation was made into the experimental conditions for the formation of poorly soluble complexes of the divalent Zinc(II) combined with the following selected amino acids: tyrosine, tryptophan, cysteine, histidine, and alanine, in the form of suspensions for parenteral administration. The number of Zn(II)-binding sites in the amino acid (n) as well as the amino acid affinity to Zn(II) (Ka), were determined. Cysteine was found to have the highest number of Zn(II)-binding sites--3, whereas alanine the lowest--1. In the conditions described herein, Zn(II) amino acid complexes of diverse stability (durability) were obtained. The analysis of the kinetics of the binding revealed that the most stable complexes were those formed by Zn(II) in combination with tryptophan (Ka = 405.78 microM(-1) +/- 12.17), and with tyrosine (Ka = 343.88 microM +/- 22.35); whereas the least stable complexes were those formed by Zn(II) in combination with histidine (Ka = 29.90 microM +/- 4.78), and with alanine (Ka = 13.0 microM(-1) +/- 1.04). Cysteine formed complexes of intermediate stability (Ka = 168.53 microM(-1) +/- 12.36). The stability ofthe Zn(II) amino acid complexes obtained was conditioned by both the molecular weight (P = 0.033) of the amino acid and its isoelectric point (P < 0.001).

125I-marked dalarelin (a modified analogue of GnRH) or GnRH (gonadotropin-releasing hormone) were administered to the tested rats in single doses of 127 ng/kg by subcutaneous injections. Dalarelin and GnRH were absorbed from the injected doses in 0.64 and 0.49%, respectively. Only one remarkable maximal concentration of these hormones was noticed in rats' blood 30 min after the administration. Dalarelin maximal concentration was 261.5 pg/cm3 and was 93.43% higher than the maximal concentration of GnRH. Dalarelin bioavailability was 1651.89 pg/cm3, whereas GnRH bioavailability was 718 pg/cm3 h. The bioavailability level of dalarelin was 230% compared with that for GnRH, which was accepted as a pattern of bioavailability.