A method of isolating a polynucleotide encoding a pre-pro GHRH polypeptide, said polynucleotide having the sequence wherein said method comprises the steps of: a) extracting total RNA from a hypothalamus taken from a dog; b) reverse transcribing the RNA from (a) using Moloney murine leukemia virus reverse transcriptase, to obtain cDNAs; c) amplifying the cDNAs from (b) by PCR using the following oligonucleotides for the reaction: NB151 (18 mer) 5'-ATGCYRCTCTGGGTGYTC-3' (SEQ ID NO: 5) NB152 (17 mer) 5'-TCATCCYTGGGAGTTCC-3' (SEQ ID NO: 6) NB153 (21 mer) 5'-GCTACCGGAAGGTKCTGGGCC-3' (SEQ ID NO: 7) NB154 (21 mer) 5'-GGCCCAGMACCTTCCGGTAGC-3' (SEQ ID NO: 8) wherein Y is C or T, R is A or G, K is G or T, M is A or C; wherein SEQ ID NO: 5 and SEQ ID NO: 8 are used to amplify a 136 base pairs (bp) fragment corresponding to the 5' end of the GHRH gene; further wherein SEQ ID NO: 6 and SEQ ID NO: 7 oligonucleotides are used to amplify an overlapping 206 bp fragment corresponding to the 3' end of the GHRH gene; d) reverse transcribing the RNA from (a) using reverse transcriptase and a Smt oligonucleotide according to SEQ ID NO: 9 and an Oligo dT 5'-CDS primer having the sequence 5'- 25N- 1 N-3', wherein N- 1 is A, C or G and N is A, C, G or T; e) amplifying the 5' end of the cDNAs from (d) according to a RACE protocol using a primer according to SEQ ID NO: 8 and a universal primer according to SEQ ID NO: 10; f) amplifying the 3' end of the cDNAs from (d) according to a RACE protocol using a primer according to SEQ ID NO:7, a universal primer according to SEQ ID NO: 10 and a SMART oligonucleotide 5'-AAGCAGTGGTATCAACGCAGAGTAC 30N -1 N-3' according to SEQ ID NO: 11, wherein N -1 is A, C or G and N is A, C, G or T; g) cloning the PCR amplified fragments directly into an appropriate plasmid; h) screening E.coli colonies by colony lift hybridization; i) identifying plasmids with GHRH cDNA using a probe having the sequence according to SEQ ID NO: 12 labelled with alkaline phosphatase; j) sequencing the clones to identify SEQ ID NO: 3. a) extracting total RNA from a hypothalamus taken from a dog; b) reverse transcribing the RNA from (a) using Moloney murine leukemia virus reverse transcriptase, to obtain cDNAs; c) amplifying the cDNAs from (b) by PCR using the following oligonucleotides for the reaction: NB151 (18 mer) 5'-ATGCYRCTCTGGGTGYTC-3' (SEQ ID NO: 5) NB152 (17 mer) 5'-TCATCCYTGGGAGTTCC-3' (SEQ ID NO: 6) NB153 (21 mer) 5'-GCTACCGGAAGGTKCTGGGCC-3' (SEQ ID NO: 7) NB154 (21 mer) 5'-GGCCCAGMACCTTCCGGTAGC-3' (SEQ ID NO: 8) wherein Y is C or T, R is A or G, K is G or T, M is A or C; wherein SEQ ID NO: 5 and SEQ ID NO: 8 are used to amplify a 136 base pairs (bp) fragment corresponding to the 5' end of the GHRH gene; further wherein SEQ ID NO: 6 and SEQ ID NO: 7 oligonucleotides are used to amplify an overlapping 206 bp fragment corresponding to the 3' end of the GHRH gene; NB151 (18 mer) 5'-ATGCYRCTCTGGGTGYTC-3' (SEQ ID NO: 5) NB152 (17 mer) 5'-TCATCCYTGGGAGTTCC-3' (SEQ ID NO: 6) NB153 (21 mer) 5'-GCTACCGGAAGGTKCTGGGCC-3' (SEQ ID NO: 7) NB154 (21 mer) 5'-GGCCCAGMACCTTCCGGTAGC-3' (SEQ ID NO: 8) d) reverse transcribing the RNA from (a) using reverse transcriptase and a Smt oligonucleotide according to SEQ ID NO: 9 and an Oligo dT 5'-CDS primer having the sequence 5'- 25N- 1 N-3', wherein N- 1 is A, C or G and N is A, C, G or T; e) amplifying the 5' end of the cDNAs from (d) according to a RACE protocol using a primer according to SEQ ID NO: 8 and a universal primer according to SEQ ID NO: 10; f) amplifying the 3' end of the cDNAs from (d) according to a RACE protocol using a primer according to SEQ ID NO:7, a universal primer according to SEQ ID NO: 10 and a SMART oligonucleotide 5'-AAGCAGTGGTATCAACGCAGAGTAC 30N -1 N-3' according to SEQ ID NO: 11, wherein N -1 is A, C or G and N is A, C, G or T; g) cloning the PCR amplified fragments directly into an appropriate plasmid; h) screening E.coli colonies by colony lift hybridization; i) identifying plasmids with GHRH cDNA using a probe having the sequence according to SEQ ID NO: 12 labelled with alkaline phosphatase; j) sequencing the clones to identify SEQ ID NO: 3.