Differential expression of LHRH-receptor in bovine nasal tissue and its role in deslorelin delivery

Deslorelin, a luteinizing hormone releasing hormone (LHRH) agonist, is transported via the LHRH-receptor (LHRH-R) and exhibits regional variation as follows: inferior turbinate posterior (ITP) > medium turbinate posterior (MTP) > medium turbinate anterior (MTA) of the bovine nasal mucosa. Differential LHRH-R expression in various regions of the nose is a potential explanation for regional variation in deslorelin transport. Thus, the objective was to determine whether LHRH-R expression exhibits regional variation in bovine nasal mucosa. LHRH-R density (B_max) and affinity constant (K_d) were determined by saturation experiments using 0.5 mg tissue in the presence of increasing amounts of I¹²⁵-deslorelin (100-100,000 cpm) at 4 °C for 4 h. The 50% inhibitory concentration (IC₅₀) was determined by competition experiments using various amounts of unlabelled deslorelin (0.01-3000 ng) at 4 °C for 4 h. LHRH-R mRNA and protein expressions were determined using real-time PCR and Western blot analysis, respectively. LHRH-R B_max and K_d varied between the regions of excised bovine nasal mucosa: ITP > MTP > MTA. The inhibition experiments yielded two IC₅₀ concentrations which exhibited trends similar to B_max and K_d. Real-time PCR and Western blot analysis indicated that LHRH-R expression exhibits similar trends: ITP > MTP > MTA. We identified two deslorelin binding sites in the nasal tissues, with high affinity sites representing approximately 60-70% of the total sites available. In summary, regional differences in nasal deslorelin transport correlate with regional differences in LHRH-R expression, with LHRH-R expression, peptide binding, and transport being the highest in the inferior turbinate posterior region of the nose.